I just spent 30 minutes posting a reply to this. I then accidentally closed the window before posting it.....
Popularity is a factor worth considering. Less popular songs are less tested.
For me it comes down to (popularity wise) am I only interested in my opinion, or am I interested in every one else's. After all I know mine. I share my perspective partly in the hope it helps someone else, and partly because it gives other people the chance to consider my opinion and offer suggestions that may modify my own opinion, my own understanding.
Another significant part is considering what people generally think. I write songs for other people as much as myself. My songs are 100% me, but 100% me connecting with other people in a musical conversation. If I want my message to connect I have to consider what other people connect to, what other people like and dislike.
In part that is the role that generally accepted songwriting guidelines (not rules) play in writing a song. They are the result of collected wisdom.
There are no absolutes.
Gijs, true, we all decide what we consider to be "good" or not. There is no alternative. What we can do however is learn from others and adjust what we think is good and why. In posting here we share our knowledge and people consider it and perhaps offer suggestions we ourselves consider and incorporate in our understanding.
If we hope to connect with others via songs, then we must be interested in what other people think. After all it takes at least two people to take part in a conversation, but it is with the speaker that the onus of being understood belongs to. In otherwords we have to make ourselves understood, we have to talk in a way that the listener will understand, and that means understanding the listener. Otherwise we are speaking purely for our own benefit.
A good song is like a good meal. You are the chef. We are your peers in the kitchen, the listener is a diner in your restaurant.
We have a list of ingredients which known recipe's tell us of combinations that have been proven to work.
So here we are in the kitchen, tasting each other's recipes. We offer our opinion taste wise, but we also have our opinions on what diners would enjoy eating. Not only that, we have our opinion on the meals others will enjoy eating so much that they talk to other potential diners about it.
As chefs we might offer tweaks to improve the recipe you create and seek similar when we offer our creations for a taste test.
There is a generally accepted wisdom on flavours, known combinations of ingredients that appeal to people. For example if I suggested adding salt, not sugar, to make cake frosting do you think most people would like it or hate it? Would you like it or hate it? I think we could all agree that very few people are likely to find it palatable. All the other ingredients and how they are combined might be perfect but that one ingredient can ruin it.
Reinventing the wheel takes time and energy that I would rather direct towards improving my own abilities.
At the same time I accept that to learn what other people like I have to listen and consider what they say. To learn what others know, I have to listen to them. My understanding is not perfect, it will never be perfect, but I can improve it.
Asking ourselves what makes a popular song also considered to have "good lyrics" is a good question to ask. And the reverse. To ask that of unknown songs is an exercise in prediction.
We have our opinion on what is good, but it is folly to not understand what others consider good and incorporate that so that our own songs improve.
Just my two cents on something that should not be overly contentious, and definitely should not be made personal or taken personally.