What's so powerfull with open limping? Raising the 33 has so many advantages, it disguises my hand since I raise all hands I play first in from any position, it can take the blinds, it takes down the pot on the flop more often than not being pre flop aggressor. Open limping and then calling a raise makes you pay the same to see the flop and you'll just end up folding to the raisors continuation bet, it's a much weaker play for sure. And if noone raises you won't manage to stack anyone if you hit your set of 3s most likely anyways, hate playing in unraised pots.