Most fights where actually rather well designed for 2 tanks.
The only exceptions where:
Durumu, and IQ. (Both where solo-tanked mostly.)
Twins: If the beasts wouldn't have been a joke, then it would have been fine. H is actually ok, if one of the tanks is on kiting duty in P1.
Lei-Shen. <- Worst in this regard.
Jin'rokh was fast paced enough, so you didn't get bored waiting for your debuffs to fall.
Horridon, Council, Tortos, Megaera, Ji-kun (H only), Dark Animus: Both tanks had their duty, so it was ok.