"I guarantee you, whether someone has learned conventional songwriting method or not, their best most liked songs will always be the ones that conform to conventional techniques the most."
Under that prescription the Vengaboys & Milli Vanilli along with a million others win hands down - a convention/trend/fashion wins everytime. Now, let's all get out our autotunes & do some of those Cher yodels, or disc scratch rhythm, or ABABABBBBBB structure or insert rap after stolen breakdown, or the latest thang.
It boils down to:
a) one's aspiration;
b) one's ability to achieve a) given nature, nurture, socio economic circumstances, parental support, world peace, DIY instructional videos and access to technology
&
c) what works for the individual.
This is all true, unfortunately.
Responding to a different post, or maybe even a different thread, ... while still acknowledging everything you just wrote, and is true,
... it's my sadness, or heart's contention, being in the smallest of subsets, ... that what passes for art in this industry, is not art at all. The art of making music, is something that artists should do. And true art, and therefore true artists, is rare indeed.
How often does a Rembrandt come on the world scene, or a DaVinci?
Likewise, how often does a Beethoven, or Beatles, come along?
So while it is true that everybody is free to think and pursue what they want (a statement not even worth making), the discussion as to what makes for a good composition is enjoyed most by those who understand composition.
One last thought before I go out for a donut - Even in songwriting, when discussing rules and formulae... had better results prior to 25 years ago. Something I wrote earlier. So, in the genre of songwriting, still, we lament over the lost culture and the individuals in the world who lack training, lack education, are not even aware of excellence, and then worse... become arrogant and consider themselves "stars" or "artists" because of a monetary or popularity achievement.
It's a conspiracy, I tell you.
