Huh, I thought they had ditched the project and ran away with the budget given to them.

Or did I confuse that to some other show?

I may be misremembering dates, but I do believe that the CalArts style was already popular enough since before "Tumblrism" became a big thing, so chances are that this is less about that and more about going too deep into cutting corners to lower needed budgets, and also probably meeting big studio demands about how to look. For example, if you look at the pilot episodes of many shows like Steven Universe and OK K.O., they actually look pretty different from each other, but the final product for both look almost identical, with the former having been the one to get nerfed the most.

Yes, both have the typical pilot episode weirdness to them, but you can tell that the art style was going for something entirely different from CalArts at first, and I can only assume that Cartoon Network did not like that.

…well, anyway, I actually care very little about the art style itself and I get the feeling that so does the OP on the image, and this is likely more about the murdering of the essence of Thundercats, which I can do nothing more than fully agree with.