well, but people like stellar and sir didnt got them "legitimate" they perhaps tested some of them firsthand and got them through that.
there are achievements where it literally was only possible to have 1 (LvP winner/loser) stellar for example has both, which isnt possible.
or the 2013 clan league first, second and third place. people only get the respective achievement to their rank, not both.
so if we go by the players who have legitimate the most achievements that would be missuse and insanity as mentioned.
but since they are partially really wonky and some were give out for certain events etc. its impossible to have them all as a player.