There's no reason to go back to Q-Manifold if you feel better in Q-Singularis though, afaik you get the same amount of crystals.

As for your difficulties in Q-Manifold, it depends, maybe last cycle you got unlucky and it was a boss with high resistance against physical, or indeed bad rotation since you have 4/4 HoS you should at least be able to retain Agony. There's also the fact that you're missing Cez B oof.

Anyway choose the one you feel it's easier, no matter if people say Q-Manifold is better. Imo it's only better if you have at least a fully or almost fully geared team, not only your dps - getting more valks for different weathers won't solve your problem, you'd be better focusing on your best team (maybe get PE or BKE and use HoS and Griseo as support? Delta does better in MA)