Thanks for the note, and welcome to MT. Couple of things stood out, that I think are pretty glaring if you focus on performance.
Oh that’s an easy one, the arts are never locked. However lots of students from said arts, who haven’t studied their style or system long enough to even scratch the surface of it decide to compensate for their own incompetence by looking elsewhere to add other styles into the mix even when the arts they are adding might contradict and
The presumption here is that the reward for diligence and patience is competence. So, at what point would someone have enough information to conclude that they aren't the issue?
hamper their progress in the main art they were trying to fix.
I broke this sentence up in the middle to highlight that you don't have to be an expert in something in order to evaluate that thing. This is a myth that gets tossed around here all the time, and it's complete bunk. In the real world (aka, everything else in the world except martial arts), people competently evaluate the quality of things all the time. Computers, cars, services, systems, you name it. All the time. You don't have to understand how a chip is made in order to evaluate it's performance.
You just have to be able to evaluate how it performs. Step 1 is to figure out what performance looks like... what are you trying to do? Learn Karate? Well, that's easy. Become an expert in kata? Okay... that's clear, too. Learn to fight? No problem. But you have to go to a school that does those things to learn those things. You can't learn to fight without fighting any more than you can learn kata without doing kata.
Point is, figure out what your benchmarks and evaluative criteria are and then apply that criteria to the system. We do that intuitively all the time.
It’s ok to practice more then one art but before you go ahead and make changes and additions to things that are usually fine the way they are, make sure you have already completely exhausted every angle of your studies in that particular style. If you don’t have a complete understanding of your primary style then anything you add prematurely will result in garbage.
See above. If you are in a system that you don't completely understand, but then add something to it that gets you closer to your goals, what you added isn't garbage. The trick is to know what you're trying to do, and benchmark your own skill level and success against your training. Is your training helping you perform better or not? If not... well, there is that old canard about the definition of insanity, right?
MMA is a great example. The goal is clear... to win fights. So, if they pick up a little of this and a little of that and it helps them win fights, it's value added. If not, it's garbage. Neither of those is dependent on being an expert in that system.... though the same thing applies. If being an expert in a system helps them win fights, it's good. If it does not, it's garbage. And you can often evaluate that without ever trying that new activity (though it's good to keep an open mind).
I look at it this way, cross training is only good sometimes. Imagine someone wanting to be the greatest Olympian ever by training Power lifting and Gymnastics and long distance running all at the same time. Well you say each of those sports or athletic endeavors may teach you sn amazing skill but do they really mix well and improve you or will you just end up with a steaming pile of crap.
Really? Are you an expert in Olympic Power Lifting, gymnastics, or long distance running? If not, based on the first part of your post, how can you possibly know? Don't get me wrong. You are doing exactly what I was saying above.... what we all do all the time, intuitively. And there is no difference in what you did here and someone in MMA saying, "yeah, that martial art system or school isn't going to help me."