AR is more like preferance imo, especially these days. All people suggest different ARs on same map from 9.0 to even 10.0.(yes I am mapping something 6☆+ though). I'm still the most comfortable with AR9, while others actually say 9.5~10.0 is actually comfortable even on same map.
idk, I honestly think AR should be adjustable and never effect pp at this level. there was a moment where people couldn't AR10 but cookiezi-level players, but nowdays.. Idk, there are people who adds HR just because they can't read 8.0, or even 9.0, and they are more comfortable with higher ARs(Just like how i do best on AR 8.0~9.3, while i can still play bit of 6~7, 9.4~s. their best is AR 9.5 and it starts from there I guess.)
sucks for them because they have to HR or DT most of old-days maps(AR9.0), or even other maps with AR9.0s.
and yeah sucks for those you can't AR9.1+ no matter how good they play.
My examples are slightly exaggerated but it does happen, though.
currently yes AR11 is known to be very hard, but what I do wanna say that AR10 was the same way few years ago. well. AR10 these days? some people actually "prefer" those.