Patch Note from 1.2.1
ĽA total of 4 mines must now be successfully defused in order to complete the minefield encounter.
Now it's definitely a gear check.
Hard mode isn't meant to be done in anything less than full Rakata.
And even in full Rakata on 8 man with 2 healers and 2 tanks we can down 4 probes.
So I would say its a check to see if your DPS are actually good or not, and a check to see if your probe launcher is fast enough, and another check on top of that to see if you can organize and coordinate well enough to do all that.