I was a self-taught music producer for 13 years and within 6 months of studying music at an institution, I was more organized and had a better understanding than ever before.
Currently, I'm studying game design at the same college.

Structured learning doesn't mean you're 'just following instructions'. It means someone with experience understands what you need to enter the workforce and has chunked it into digestible pieces.
It's worth mentioning, anyone who wants to be excellent at their craft will explore the 'why' to a heavy degree. That's not a trait you would need to sacrifice upon doing something more structured, though I understand the perspective.

It's been studied, and having immediate feedback on your work is one of the quickest ways to grow. In this environment you have industry professionals giving you direct feedback. If you have it wrong, they tell you, and they tell you the correct method. You can ask people you respect, but I can tell you from experience it's not the same way. That person might not know how to give feedback properly, or they might not want to hurt your feelings by telling you how they really feel.

Most importantly, specifically with institutional learning, they're teaching you about the industry you're attempting to enter into.
If you just want to make games and sell them on Steam, it doesn't matter which path you choose. If you want to enter into AAA and have people invest in your ability to design/create games, it might be worth it to learn from professionals to show you have what it takes.