I ran Grotesques in the beginning and they did okay, but at any rate they should be used with a Haemonculus. T6 makes a big difference if you send Grotesques after things that are not your average MEQ.
However, the biggest advantage for this configuration is that your HQ is more than just a tax. Haemy has a great aura and his combat potential are very reasonable. Do not underestimate the Electrocorrosive Whip.
Especially if you used an Archon as HQ before, you have your points spent much more efficiently imo.
Nonetheless, I found more success in running beasts. Especially Clawed Fiends give you a lot of mileage (AP-1, D2, dont need transports) and cost 25% less.