if you are orb with hydra, you don't even need a sunder. if you get monsters immune to both, just move on.
Does it mean no more infin? right?
or does more damage come from conv then i know?
Yes, in theory, no more infinity. But infinity even without the lightning immunity removal is still a good merc weapon. 40 crushing blow lol, plus the rest.
No, there should not be more dmg from infinity with conviction and a sunder charm. Sunder works first, removes the immunity, then the conviction works the same imo.