Realism is not the only qualifier for what is and isn't good art.
No, but it's a core aspect of an entire school of animation. It's fair to say that it's the only thing Thundercats had going for it, in fact. Watch a few frames; unless we're talking about Snarf, pretty much every character on there is drawn is if they're in a state of permanent flexion. It is, effectively, what makes Thundercats Thundercats (aside from Lion-O's extremely peculiar gender ambivalence).
Look. Seen Metalocalypse?
That's an homage to an aesthetic common to death metal bands. It captures the metal scene well enough to make the visuals a joke of their own. Seen Moonbeam City?
Me, neither. I hear it's terrible. But I can look at that and know that they're shooting straight for a Patrick Nagel/Miami Vice/Gem & The Holograms '80s such that the artwork probably sold the series alone.
And you don't need to know what the fuck a "thundercat" is to know that there should be some thunder, and there should be some cats. And for those who give a shit, what they've got so far is more like whoopie cushion jelly bean.
If you love Sailor Moon, you would want a Sailor Moon remake to look like Sailor Moon, not the Power Puff Girls. Ostensibly, the only thing that separates the two shows is their aesthetic. And the outrage is about "fuck your aesthetic, we're drawing jelly beans now."