I don't think the adds have 50k hps. I was killing them instantly with each cast of Tectonic Destruction Rank II and even with crits that doesn't do 50k per shot.
Wiped tonight with monk, enchanter, beastlord, wizmerc, clrmerc, tankmerc. Adds are very squishy. We neglected them at the end to burn named and ended up doing us in (LOTS spawn). I recommend just keeping the adds under control.