l personally don't rely on these assets at all to make my game, I can make my own models. If I find something useful in there, I'll use it, but I won't spend the 10 days on that.
It's not about being spoon-fed. We can't blame Unreal or Unity for being popular, but we could blame them for using non-standard formats to keep their assets exclusive. Its also a limitation of audience for the asset creators.
As for using AI... It's a vast topic that may be on the border of copyright infringement.