Then it would be caused by differences between the Lutris installer and PoL installer, not Lutris itself…
The default installer for LoL used the OpenGL renderer which might have different performance than the DirectX renderer. I also published an installer for the DirectX renderer as well, didn't try it, I don't play LoL.
I remember having played World of Tanks once, didn't notice any particular issue.
You're basically judging the quality of the platform on 2 games which might have been set up differently than what you've experienced in the past. As far as I'm concerned, there is absolutely no performance hit caused by Lutris itself. It's up to the community to provide the best installers for games, submissions are open to any registered user.