As I said, theory is descriptive, not prescriptive. People can "not know theory" and have an extremely good ear. Look at Dave Grohl as an example. He is a successful musician with no knowledge of theory. He has a great ear and worked with probably one of the greatest voice leading artists of the last 30 years. Even better, Michael Jackson wrote every part of his songs by singing them and had no knowledge of theory, yet music theory can explain his chord progressions and melodies.that's not what I said at all. but lets be real, I've lost count of how many metal/rock guitarists I've seen interviewed that confess , they know zero theory, there is a generation of players out there right now that seem to embrace learning theory more than in past days but there is no shortage of famous players that don't really know much theory at all.
And I will disagree with you that knowledge confines you in any way. Once I really started to understand how to play modally my palette completely opened up. when I hear guitarists "improvising" and all they know is Pentatonic and the occasional flat 5 "blues" note thrown in playing over dominant chords I know their knowledge is limited.
In terms of modern metal, if you think people like Jason Richardson, Tosin Abasi, Per Nilsson, etc. Don't know theory, you are just basing your view on you own biases.
The main thing that music thoery gives you is a way to convey ideas to other trained musicians quickly. That can include techniques like "play this scale over the dominant chord". That statement doesn't contain any theory, it contains a description about how to get a certain sound. You don't have to play just that scale. You can play anything else.
If you learned modal playing, you could have just as easily been told to play certain shapes over certain chords (which is how jazz is usually taught, play scale x over this dominant). People doing this usually have no idea why that shape or mode makes any sense over that chord, but they practice it. Same thing for boxing, most jazz musicians have no idea why boxing works, they just learned it as a technique.
I had an interesting conversation a few years ago with one of the best jazz pianists I know. I asked him if he could give me jazz theory lessons and help me understand how he was approaching his lines. He answered: "I don't know theory, I just play what I hear in my head." When you think about it, this is a hallmark of jazz, improvising on the spot. Taking patterns, licks, and shapes, then trying to play them quickly over chord changes. Most of it by definition is unplanned and not based on theory. It is based on practicing lines that other people use without thinking about why it works. Theory can be used to explain why some things work, including the accidentals.
Another way to look at it, the augmented 4th is usually considered dissonant, yet it is used all over the film score industry as a strong chord tone as a Lydian chord. The reason is because it is the second harmonic of a major 7th. So if you play it with a major 7th, it can be explained away as consonant even though blues and jazz musicians would never view it that way. By associating it to a style of music without understand the fundamentals of why it works, theory is restrictive.