Plasma is more lightweight than GNOME in terms of resource usage, so.... (I use a tiling window manager, btw)

I've been using it for a long time. I've personally found that there is essentially no impact on gaming performance--or if there is, it's so slight that it's totally negligible on midrange hardware, especially with feral gamemode. It might be more impactful on low spec PCs, I would assume, but I'm not sure of that. In my case, it's plenty lightweight and offers lots of customizability.

I used to feel that way as well, but things have changed and improved quite a bit.