Whether it's off topic or not sort of depends on whether you believe formal education, particularly in notation and reading, is necessary for a person to have a strong grasp of theory because a lot of people would tell this person I know that he doesn't know any theory at all. But I'll stop now.
Firstly my apologies for miss understanding your view point.
As to do we need THEORY, the answer is still yes. Like lots of subjects I think people shy away from "high brow" lots of technical words, "it sounds difficult therefore it must be".
As I said before loads of musicians, and I use musicians deliberately, run around key changes, modes, transposing and a 1001 other things "BUT DON'T KNOW THEORY". What they really don't know is what the technical term is for what they just did.
Again, as I hope you picked up on, I do not support the theory in a class room arguing is it this or that, stupid point scoring. In a practice or open mike and someone shouts R&R in G - off you go, someone turns to you and says can you walk on the Pentatonic?
The theory is done in your head in a flash - Yes Im in ?? now so if I use the leading note and then walk down the scale back to the root of the next bar.
Its all theory, if you then want to describe what you did in a way that every one understands NOT well I 4-4, 3 -4 and dropped a string to the !!!!!! etc etc etc. I know a lot of keys players will be sitting boggle eyed. But you could have explained the notes to a German Violin, A Lebanese Sitar, or an American (no sorry not American because you all speak different musical terms QUARTER Note, 1, 2, 3, 4) OK OK I was only joking, but the American guitar player would understand it as well.
And just to get myself out of trouble, I was taught to use the American by an Australian musician and have to say how much easier and obvious it all is.
Whatever - ENJOY WHAT YOU ARE PLAYING.