Trad theory will enhance existing talent but do nothing for people who have no instinct for music, no matter how much learning they do.
It's very directly and obviously useful for certain kinds of music, especially Hollywood pastiche and some genres of game soundtracks.
It's also very handy in some areas of pop. Pop's dirty secret is that a lot of it is written/arranged by professionals with some kind of classical background. The lead band/artist are typically front people for an entire team which includes a producer, various engineers, and possibly session players and arrangers. These people don't get a lot of attention, and only industry insiders have heard of them. But they have a huge impact on pop of all kinds.
Vocal harmonies, string parts, and sometimes brass parts have to be written and arranged, and that's a challenge for anyone without dot-writing skills.
But there's also a kind of fluency and ease that comes with solid training, and that spills over into vocal and instrumental contributions of all kinds.
Trad theory on its own doesn't guarantee interesting or successful music. There are plenty of composition graduates who have no feel for the art of music at all.
It also doesn't help with transformative developments and new techniques.
But it's far from useless. People with solid theory skills and some creative flair are in a sweet spot that's hard to beat.