It's about not putting the cart before the horse. Theory is a guide to the songs, not a set of rules to be mastered in isolation.

In philosophy there is a test of necessity and sufficiency. Theory is definitely not sufficient to become a proficient musician (let alone a composer). I think it is arguable whether or not it is necessary (I would argue not and handwave towards the list of musicians who are literal legends despite 0 theory). So as a strict answer to your question: maybe not.

However, practically, learning some theory is obviously beneficial to many learners and can speed up the process of acquiring the skill. But again, beware of cart before horse.

Take one famous legend who is infamous for his insistence he know no theory: B.B. King. I mean, anyone who analyses his music can point out a laundry list of complicated theoretical things he is doing in his playing. He just doesn't know the "book names" for it since he learned those things in a different way. He definitely know what a "6" chord is, when to use it, what scales to use with it, etc. But if you asked him to explain it to you he'd probably show you 4 or 5 songs instead of writing you an essay.