That is only true to some extend. A lot comes from not optimized mods. I hear so often, that the game is not optimized, but hell,.. current hardware should have no problem with it. My worst example was a god damn accesory, that was cutting my FPS down to 30% when used, took me a while to find it. And lets not even talk about textures ...
I wouldn't blame new creators, but some of the worst are the established and praised ones, that should have learned by now.
Sometimes you gain some performance, just by finding the char that's causing it or the item used in studion