I think you're overvaluing /co/ in this argument, friend. While you're not wrong, popularity on the internet doesn't make a show "important" on its own. MLP likely wouldn't even exist without Adventure Time. I will admit, however, that it deserves a spot on the list. If I had to rank them by influence, it'd be
1. Adventure Time because of everything already stated in this thread
2. Either Rick & Morty or Bojack Horseman (probly bojack because it's also a Netflix show and is generally more innovative, but I think Rick & Morty came first, not to mention its much more popular thanks to /leddit/ etc) because of how they flipped storytelling in adult animation on its head and integrated emotional complexity and seriousness that until then had only been seen in fringe shows like Moral Orel. Basically, these shows are responsible for the rise of the "adult animated dramedy."
3. MLP, for the reasons you list as well as for how it broke the mold and is still breaking the mold in conjunction with its unorthodox and controversial fanbase. As a show, it's honestly not that innovative besides proving that a licensed "girly" show can be a full product with artistic integrity and mainstream appeal--which is nice, but doesnt really involve the show itself, if you get my meaning; "being good" isn't exactly *important* out of context, whereas both (all three) of the above examples did something that had never been done before and inspired countless undeniable trends and standards, in ADDITION to being "good" shows.
I think it's only right to mention Gumball, too--it's still too early to track its influence, but everything points to it being a trendsetter. That's more or less conjecture, though.