>>21316173Steelix was rarely offensive, it GSC at least it worked as tank.
From Gen3 and forward its best and main role was phazer and sleep talker.
It still is. M-Aggron offers a better bulk and typing, the ability and movepool are also superior to Mega Steelix, plus having less weaknesses and chance to be a sort of mixed wall are a big plus.
Steelix is definitely outclassed by Mega Aggron at least in this and maybe even on the full offensive side too.
Steelix beeds some special features like Glare or Coil or just Thunder Wave to be slightly better (probably won't have those because it was most likely based on a worm rathet than a reptile). It would have enjoyed Iron Barbs or other solid abilities too.