All the 2.0 HM primals can be solo tanked. PLD for Ifrit, either tank type can do Garuda. Titan never needed two tanks.

Garuda Ex can be solo tanked (there is a video) but you have to out gear it so bad it isn't even funny. Titan and Ifrit Ex, Ultima and Mog need two tanks. Coil has plenty of two tank scenarios.