On the server side, you could check for abnormalities in a person’s stats, for example if they get >90% headshots, if they’re getting a lot of kills outside a weapon’s normal range, amount of time aiming at enemies through walls that they shouldn’t be able to see etc etc

That's called heuristics and EAC does that as well. Why not do both?

Not saying there shouldn’t be any clientside anticheat at all but at the point of the anticheat putting itsself in kernel space it’s gone too far

Why? this isn't the opinion of a lot of the players out there.