Do you agree with this statement:Personally, I don't see how any true martial artist could perfect his/her craft without those 4 mastered or to its pinnacle. If you disagree, what do you think are the most foundations of martial arts?
The 4 cornerstones of martial arts: flexibility, endurance, speed, and power. In that order.
Note: by martial arts, i don't mean only east asians fighting styles. I mean fighting style from anyone in the world: muay thai, boxing, fencing, etc.
They are certainly required, but they aren't sufficient, and I would seriously argue against the ordering. For a Brazilian Juijitsu practitioner, endurance is key. For a Western Boxer, speed and power are the most important. I used to study Tae Kwon Do with a guy who was not very flexible at all, but could still "kick you in the head if [he] wanted to" (he'd punch you in the stomach first to make you double over).
I think any "true" martial artist is anyone who takes the study of physical violence very seriously. You're a martial artist on your first day of study if you're truly serious about it and cognizant of your limitations, as far as I'm concerned. And I think any "true" martial artist is going to figure out their strengths and weaknesses and minimax optimize accordingly, while also trying to work out those weaknesses. Style isn't that important, as Bruce Lee said, "Before I learned the martial arts, I thought a punch was just a punch and a kick was just a kick. After I learned the martial arts, I knew a punch was just a punch and a kick was just a kick." It's how you employ your technique in your own context that is important.
As for sufficiency, you missing knowledge, you're missing awareness, you're missing ethics, you're missing metal, and any number of things that go in to making someone a competent fighter. Any "martial artist" who discounts some area in favor of others is missing the greater point of martial arts: it's not about fitting an ideal, it's about creating an ideal. Jet Li and Jason Statham are completely different sizes of people, their fighting styles will necessarily be different. ALL aspects are important, and they are equally important, but we don't have the ability to focus on all of them, so you have to choose what fits for you.
So no, I would not say your statement is at all accurate.