Pleasantly surprised that Arch tops the chart. Then again, and I might be wrong about this, but to me a clear bias in the ProtonDB data is that those who submit reports to ProtonDB are usually users who are likely used to submitting bug reports and stuff, so obviously not your average "freshly migrated from Windows" gamer.
Arch is very powerful and flexible, but definitely not newbie friendly. I only made the jump after 7 years of using Ubuntu and Debian, and I still had a learning curve.