Go look at archives of threads from a few years ago. The eyes and faces, which I already pointed out, are still very similar here. You're an extreme newfag if you think "calarts style" didn't exist before the beanface thing. It's existed for decades. That said, it has evolved over time, and in more recent years, shows have become more and more same-looking.
You realize it refers to styles and techniques taught at an actual school, right? The complaint is that those styles and techniques are becoming more and more dominant, with students not being creative enough to branch out, and others who weren't even students copying it. Of course part of this is the school's fault, for not encouraging more creativity, not to mention skill, which goes along with the other complaint of the school teaching an ugly style that doesn't utilize what used to be considered fundamental skills.
Frankly, it's not as if the school isn't itself influenced by other industry trends, so you can certainly trace the influence back further than CalArts, but the point is that CalArts is a major school that teachers this shit, and fails to teach useful stuff, but is incredibly influential and has been for decades, so its clout remains even with modern complaints. See A113 references in tons of cartoons, all referencing a specific classroom number at the school.
If you were going to try to trace it back further, you can obviously see the style evolving through cartoon network shows going back to the '90s, and you can see it evolving in different directions if you follow the careers of people who worked there in those formative years. The influence of their time working on shows like Dexter's Lab can be seen in the works of both Butch Hartman and Seth MacFarlane, even if they're relatively different, at least compared to today. And are you going to say you don't see any influence of Seth MacFarlane in the very Pre-Rick & Morty cartoons you just referenced? Of course the early Cartoon Cartoons were influenced by John K., who was hired (after being fired from Nickelodeon) to help launch Cartoon Network's original content. He was strongly influenced by Hanna Barbera, and of course CN was basically the Hanna Barbera channel to begin with, with their early shows straight up being HB shows, so the influence is obvious. In a way, you could say the modern "calarts" style is the eventual evolution of the Hanna Barbera style, but I think few would say that since it evolved quite a bit over the course of the 2000s, but by looking backwards through the history of shows, you can see the evolution.
But that last part is all moot, because it's called Calarts because Calarts promotes it. And none of it changes the point that a minor change on a recent addition to the formula doesn't make it a wholly different formula. Next year the formula will become even stricter as suddenly every character will have to be black or something, and you'll look at Star vs The Forces of Evil and say "see! It's not CalArts because they're not all black!" They're just getting more and more specific, lowering your standards further, and leaving plebs like you thinking that the most minute way it doesn't follow the formula actually makes it different.