I was doing everything "wrong", from a technical point of view. I never learned any theory, I never used my fourth finger, I never learned alternate picking... Perhaps if I learned some piano it would help with the theory?
OK - first off: You seem to be conflating the study of theory with the study of technique, which we generally call method. They are too different disciplines. Method means the mechanics of how to play an instrument, and each instrument has its own method for mastering it. Theory is not really specific to any instrument at all, and you don't even have to be a musician to know musical theory: Theory means the guidelines and vocabulary we use to describe our music in the abstract: Chords, scales, keys, intervals, etc. etc.
Great theoreticians don't have to be great musicians, and great technicians - masters of technique on an instrument - don't have to be great theoreticians, although each area of expertise certainly compliments the other.
I never used my fourth finger, I never learned alternate picking.
These are not questions of theory, but of method.
So again:
Perhaps if I learned some piano it would help with the theory?
As far as the study of theory goes, piano is essential. Every serious musician should know at least basic piano, to facilitate the study of theory. The visual nature and the keyboard layout of the piano make it ideal for studying theory, however studying piano will not help much when it comes to using your fourth finger on the guitar.
Today, basic theory is arguably mandatory for any musician with aspirations of advancing beyond the level of a stay-at-home hobbiest.
The question of theory stifling creatity has been bandied about endlessly by untrained musicians, and comes up on this site from time to time. Here's recent question dealing with it:
can music theory sabotage creativity
Having said that, your question actually seems to focus more on method/guitar technique than on theory, so let's address that:
Making music is about expressing yourself. Formal technique methodologies are tools to help musicians express themselves - they are not iron-clad rules.
Similar to musical theory, no matter how many youtube videos and books and teachers preach their methodologies, there is no absolute "right" or "wrong" when it comes to technique. The issue is simply what techniques - which method - help you to express yourself on your instrument in the most fluent way possible.
Formal methodologies for various instruments - such as using the fourth finger - were developed as knowledge accumulated about what allowed musicians to create better, more expressive music more efficiently and adroitly. Nobody handed down any divinely inspired laws about how to play music.
In addition, not everyone's body/hands are the same. There may be certain recommended techniques in books that are very difficult for some people to execute. Would it be worth it to spend years trying to perfect such a technique when doing so precludes you from expressing yourself and enjoying music the way you would like to? In the vast majority of cases, the answer is a resounding No.
It is true that if you are just starting out, learning the accepted rules of formal technique is a good idea - one learns things that help you play more efficiently and effectively and can be leveraged as you develop into a mature musician. But invariably, even those with a lots of formal training in technique will develop their own approach to technique (although it will incorporate much of their formal training) as they mature: the approach that best suits them for expressing themselves with their music.
There have been many good, even great musicians, who, just as they knew little or nothing about formal musical theory, also knew little or nothing about proper technique. They were self taught and figured out how to play the way they needed to in order to express themselves through their music. People like Jimi Hendrix, Wes Montgomery, Paul McCartney... the list goes on and on...
He did not learn this in music school:
Thelonious Monk did take formal piano lessons as youngster, but discarded virtually everything he learned as he developed his own extraordinarily unique style that required something else entirely:
Monk:
Nonetheless, they were great musicians because regardless of their technique, they were able to express themselves in eloquent, unique and appealing ways through their music, which is what ultimately makes for a great musician.
Bottom Line:
You are in a situation where putting aside what you did before and trying to learn formal technique is preventing you from expressing yourself musically the way you want to. In your case, formal technique is not serving its proper role. So: IMO forget about formal technique and play in the way that facilitates your own ability to express yourself musically - the goal of every musician worthy of the title. Go and play your old punk-rock technique for all its worth - enjoy yourself and let it all hang out.
BUT: That does not mean that you should ignore and forget what you've learned about formal technique. Continue to pursue that study - "book learning" never hurt any musician, when it's applied properly. They key is not to force yourself to incorporate it into your personal playing style. It should work organically: Don't change your musical identity because of what it says in a book.
What will happen over time is this: As you are doing your thing, certain aspects of what you've learned about formal technique will find their way into your personal style, in ways that will help you. You will integrate them into your style because once you know them, you'll find ways to use them to help you play your own music.
