I am 4 digit in osu! (top 2k in USA) with 600 hours in the game, and I have 600 hours in kovaaks (an aim trainer that's literally just the same as aim labs) and I've hit like 140k on gridshot. Both of you looked past a very important mechanic that's most prominent in osu!, which is "reading" Being able to train my eyes to look at notes across one side of the screen to the other and flick to it was a big learning curve when I was climbing the ranks of osu!, and it was a skill that took a lot of time. In layman's terms, just look at this clip of XQC watching the top osu player https://www.youtube.com/watch?v=-yun9lwaay4 You don't need to play the game to realize that you need to read and react to the circles extremely fast. I also think the osu! maps I"ve played require more speed aim than just hitting 100k on gridshot. Playing osu! with the DT (double time) mod means I have aim way faster than I would to have to hit 100k on gridshot. Also I think using gridshot as a benchmark feels wrong when you use it to generalize the actual aim mechanics of fortnite or csgo. Trust me, sitting in aim labs or kovaaks all day to become a god at whatever FPS you are trying to train for just won't work. I was hardstuck plat in valorant even though I was "grandmaster 1" in aim labs and I was grandmaster in the static scenarios in the Voltaic benchmarks for kovaaks (which are a lot harder and more practical for valorant than gridshot). But I didn't finally get immortal in valorant by being an "aim god" but through game sense and being consistent with crosshair placement-- which are also hard mechanics, I'm not trying to undermine them. But even though osu! just requires "2 keys" to use, you have to quite literally train your hand muscles to play the hardest maps. It's not "just timing" when your eyes and hands need to literally be trained to play the hardest maps. There's more but that's at least why I believe osu! is the "hardest" game mechanically. I mean there's literally no limit to osu! so it has got to be the most mechanically demanding game out there.