Martial arts are about skill training. To that end, you see a lot of strange opinions on fitness from martial arts instructors who are clearly unfit. It's a little bit of an odd dynamic.
Fitness can be defined. It's a combination of attributes, all of which are trainable, and it goes like this:
I should add, that list is in no particular order of importance; that is, until you don't have one of those points covered off, then that is number one in your world.
Or, at least, it should be. If it isn't, then your training really doesn't make all that much sense from a self-improvement view.
People hide their weaknesses from the outside world, play up their strengths, and basically go on living whatever illusion they have going on that best serves their respective schema. It's a type of mental masturbation that is ultimately used to justify inaction at shoring up a deficit or straight up camouflaging a liability.
Weak martial artists will tell you technique is the most important thing. Athletic martial artists will tell you fitness is essential. The truth is, none of them and all of them are important, but it's a sliding scale depending on what you are bringing to the table in the first place.
If you look like you've never touched a weight in your life and you struggle to do double digit push ups, stop talking. I don't care what your opinion on strength versus skill is because, let's be honest, you only have one and it will fail during a serious pressure test.
By the same token, if you are built like a rugby all-star and like to make fun of "scrawny" martial artists that you like to think you would squash like a bug, you need to spar more. I have friends well under 200 who would light up the 200+ crowd without too much trouble.
But when you train it all? Well, that's different. Competent martial artists who have strength, endurance, flexibility, mobility, and capacity are truly rare animals and worthy of respect. Add size to the mix and you get someone who can probably make a legitimate run at being a professional athlete.
So let's not get too carried away with skill versus size versus strength versus prayer beads or whatever else. There is an antidote to everything, even when you have it all. Your best approach is to see it all for what it is, see yourself for what you are, and learn to put the pieces together in a way that makes sense for what you're doing.
Leave the masturbatory pseudo-intellectualism about what's "most" important to the men and women hiding a weakness or, more likely, weaknesses. The absolute bottom line is that anything you don't train is a liability and that any advantage that you over rely on is also a liability.
Yes, that includes skill.