Dark, soo and Byul are able to cope with top Terrans better, from early to mid to late. They're great in mixing things up. Maybe that's why they fare better than Life (who's more one-dimensional in the current meta).
Though Inno's mech look abusive as hell in this series, I'm not sure if it's imba vZ. Inno's TvT mech looks pretty strong too, and he's able to take games even when behind (e.g. recent game against Flash). I think Inno's mech is just a cut above the rest, at the moment.