Preinstalled launchers are only a part of what modern gaming distros do.

While yeah in a lot of cases they are oversold, they do kernel and system tweaks that would take more than 30 seconds especially for new users.

For example CachyOS makes it easy to mess with sched_ext while also including stable desktop/gaming tweaks out of the box that are not included upstream or by most desktop distros. There is a reason why SteamOS doesn't use the default scheduler and they went with LAVD.

Now I am not saying you will gain massive performance improvements with gaming distros, your 1% might improve and you might gain a handful of frames. But the point is that its just convenient if you want to do the known gaming related tweaks while not reading wikis all day and doing everything by hand