[JansjoFromIkea]

Slop is an unfair word to use, agreed.

I suppose it's possible that they're viewing those factors as being inherent in the original Quake engine rather than something Valve should be credited for and relying on them in their fork so heavily when it didn't suit the overall game was a bad mishmash.

It's more likely they're just conflating how ugly a lot of those later levels are with the engine.