The notation OP is using is relative to the key of your song. So if your key is C major, the V chord is G. However, if your key is F major, the V chord is Bb. So it's not that there's only a few chords used in popular music, it's that there's a very consonant group of chords for any key your choose.
Also, OP is leaving out lots of ways to modulate these basic chords into more complex ones (adding a seventh step, inversions, power chords, etc.).
Finally, as with a lot of pseudo-Pareto type things, often the few exceptions are what make or break a piece musically.
Any suggestions about theory learning beyond this?
Something that would help with composition perhaps? Music phrasing? Some book to read? Something for self learning? I wish that melodies I am trying to compose would be better in reflecting what I like in music, and I whish to figure out what is missing.
I can improvise with different chords but it is getting boring and once I try to do something more comlex it doesn't reflect what I like.
I think I am missing something basic and simple but since I had no other option but to learn myself mostly it is probable that I simply wasn't exposed to something essential in theory, something that all good composers know very whell, something that allows experimenting but in a productive way.
May be there is a book that is like a bible for all composers and I simply never heard about it?
I don't have any specific recommendations and am quite rusty - but years ago when I was similarly interested I just looked up a decent undergraduate music programs course requirements and got their intro harmony text followed by intro comp text; learned a lot from that.
Also, OP is leaving out lots of ways to modulate these basic chords into more complex ones (adding a seventh step, inversions, power chords, etc.).
Finally, as with a lot of pseudo-Pareto type things, often the few exceptions are what make or break a piece musically.