You're right, the achievement is aimed for iLvl226 players.
Blizzard didn't intend Sarth3D to be doable this tier. There's blue posts saying "this is tuned for T8/T9 level gear".
Anyway, for my 25 man guild, with our best team, it took us around 10-15 hours of wipes. It's not an easy encounter.
Put it this way, once you've done it - you completed WoW (for now). Do you really want it to be easy?