I would to a degree, disagree. Lol
While not always entirely accurate, as pauses are hard to determine the length of in some circumstances, you can compare relative rhythms with some success. The reason is "scansion". In essence this is the rhythm born from the natural phrasing of speech. Certainly that can be affected by the rapper or singer's accent, but the words and phrases tend to be affected equally. This means that while reading a song you may not get the exact rhythm used by the performer, you are likely to be close.... Especially if the writer takes the time to format the song so that their words are laid out in basic rhythmic blocks writers call lines, verses and other section types. That is precisely what laying it out helps with.
If you write it out as prose, as many rappers do, it robs it of that communication of rhythm, instead relying on the less precise rhymes to set the beat. I say less precise because an individual line might use internal rhymes which can muddy the rhythm in prose.
Scan is our biggest clue to rhythm. Rhyme helps to accentuate the key beats. The written lines and multi line blocks help further communicate rhythm.
My point, is that for critique purposes the word is written, not spoken. The rhythmic problems you describe exist for all song forms, not just rap. I can understand that rappers may look for feedback on concepts, tricks of language and flourishes, but just because they have not learned to communicate rhythm when writing, does not mean they can't, nor that in doing so that it wouldn't be a worthwhile benefit.
I repeat, the issues you describe exist in all other written art forms from poetry to songwriting, including rap. In poetry it is called meter.
Out of interest scansion is hugely important. Even sung we almost always phrase things in the same rhythmic patterns we use when we speak the same words. Sure tempo may be faster or slower, but the rhythm is essentially the same whether we speak, rap or sing. Of course when we sing or rap we also block words and phrases together and then perform that in relation to a backing track that contains at least a backing rhythm and usually some other musical elements like melody and harmony etc.
I have heard some excellent raps, and I have heard many terrible raps. One of the several key points is that of the rhythm used. Get it wrong and it can trash a song as easily as a cheesy metaphor and weak or overdone rhyme scheme.
Look at "I'm back" by Eminem (fair use for learning purposes)
[Chorus: Eminem repeat 4X]
That's why they call me Slim Shady (I'm Back)
I'm Back (I'm Back) (SLIM SHADY!) I'm Back
[Eminem]
I murder a rhyme one word at a time
You never, heard of a mind as perverted as mine
You better, get rid of that nine, it ain't gonna help
What good's it gonna do against a man that strangles himself?
I'm waitin for hell like hell shit I'm anxious as hell
Manson, you're safe in that cell, be thankful it's jail
I used to be my mommy's little angel at twelve
Thirteen I was puttin shells in a gauge on a shelf
I used to, get punked and bullied on my block
'til I cut a kitten's head off and stuck it in this kid's mailbox
("Mom! MOM!") I used to give a - f*ck, now I could give a f*ck less
What do I think of suc-cess? It sucks, too much press I'm stressed
Too much stares two breasts, too upset
It's just too much mess, I guess I must just blew up quick (yes)
Grew up quick (no) was raised right
Whatever you say is wrong, whatever I say is right
You think of my name now whenever you say, "Hi"
Became a commodity because I'm W-H-I-
-T-E, cuz MTV was so friendly to me
Can't wait 'til Kim sees me
Now is it worth it? Look at my life, how is it perfect?
Read my lips bitch, what, my mouth isn't workin?
You hear this finger? Oh it's upside down
Here, let me turn this motherf*cker up right now
[Chorus]
[Eminem]
I take each individual degenerate's head and reach into it
just to see if he's influenced by me if he listens to music
And if he feeds into this shit he's an innocent victim
and becomes a puppet on the string of my tennis shoe
[vocal scratches] My name is Slim Shady
I been crazy way before radio didn't play me
The sensational [vocal scratch "Back is the incredible!"]
With Ken Kaniff, who just finds the men edible
It's Ken Kaniff on the, internet
Tryin to, lure your kids with him, into bed
It's a, sick world we live in these days
"Slim for Pete's sakes put down Christopher Reeve's legs!"
Geez, you guys are so sensitive
"Slim it's a touchy subject, try and just don't mention it"
Mind with no sense in it, fried to get so frenetic
whose eyes get so squinted, I'm blind from smokin 'em
with my windows tinted, with nine limos rented
Doin lines of coke in 'em, with a bunch of guys hoppin out
all high and indo scented (inhales, exhales)
And that's where I get my name from, that's why they call me
[Chorus]
[Eminem]
I take seven (kids) from (Columbine), stand 'em all in line
Add an AK-47, a revolver, a nine
a Mack-11 and it oughta solve the problem of mine
and that's a whole school of bullies shot up all at one time
Cause (I'mmmm) Shady, they call me as crazy
as the world was over this whole Y2K thing
And by the way, N'Sync, why do they sing?
Am I the only one who realizes they stink?
Should I dye my hair pink and care what y'all think?
Lip sync and buy a bigger size of earrings?
It's why I tend to block out when I hear things
Cause all these fans screamin is makin my ears ring (AHHHH!!!)
So I just, throw up a middle finger and let it linger
longer than the rumor that I was stickin it to Christina
Cause if I ever stuck it to any singer in showbiz
it'd be Jennifer Lopez, and Puffy you know this!
I'm sorry Puff, but I don't give a f*ck if this chick was my own mother
I still f*ck her with no rubber and cum inside her
and have a son and a new brother at the same time
and just say that it ain't mine, what's my name?
[Chorus]
[Eminem {vocal scratching}]
Guess who's b-back, back
Gue-gue-guess who's back (Hi mom!)
[scratch] Guess who's back
[scratch] Gue [scratch] guess who's back
D-12 [scratch] Guess who's back
Gue, gue-gue-gue, guess who's back
Dr. Dre [scratch] Guess who's back
Back back [scratch] back
[scratch]
Slim Shady, 2001
I'm blew out from this blunt (sighs) f*ck
First thing you see is that it is blocked out in verse, chorus and other sections. Second you can see that within a verse that too is laid out in lines. Those lines give the key rhythmic statements.
Next you can look within the line and the emphasis through the use of alliteration, rhyme and other accents, where emphasis is placed within the line. Additionally we can see how rhythmic pattern are repeated as hooks through the song. That level of detail is as important as the metaphors, the emotion or the story when it comes to writing well.
My problem, in all honesty, when I look at rap that isn't formatted in this way is that the writer hasn't learned the importance of this level of detail, and that it is an indication of their lack of experience as a writer.
This shows in writers of all kinds in different ways. For some reason in rap the myth that detail is unimportant is shown, often, by thinking that somehow it is such a different art form that suddenly the rules of language aren't helpful or that writing them down is of limited help (limited to concepts, metaphors etc)
The fact is if they can't appreciate the detail in the written word, then usually they miss it in the spoken word and vice versa.
To me I think much of it is that it involves rules, and somehow writing it seems too much like hard work. Fact is, to hone what we do, to turn it from mediocre to amazing, we NEED to care about the detail.
Hell, if Eminem can do it for his songs, surely other rappers and hip hop emcees can do it too knowing that it can be done.
In truth, I just don't see in any shape or form why rap is any different from any other form of lyrics and songwriting. It isn't. Rap is the combination of words and rhythm. Add in melody (it exists even when words are not sung, in the same way drums can convey simple melody). How is this different from any other form of song writing. It isn't.
In exactly the same way that other lyricists can benefit from a close and structured analysis of what they do, so can rappers. Telling yourself it isn't so doesn't make it true. Continuing not to just continues to miss the detail, or even why that detail is important.
It is easy to keep focusing on the obvious. That too is true for any art form. As any musician can tell you that gets passed the basics, to improve take focus on the detail, otherwise you are always a beginner in terms of performing that instrument. True you can progress at metaphors or the use of interesting progressions, but you miss getting good at licks and much more. So yes get good at the story and the emotion and the tricks, but to get it to all hang together as a complete piece rakes an eye for detail. The ability to spot what is breaking a piece, or what is missing, takes knowing detail. Using structure, line and section, helps you to do that. No question.
If you can't communicate it in writing, you don't truly "get it". If you don't get it, you will never use it to it's most effect. Can you get pretty good? Sure. But you will miss being amazing.
As a rule, if it is hard to do, it is often worth it. Not just because of the destination, but because of the journey to get there.
Just my two cents.