It's been a long while since I've watched the episodes but I thought one of the most devastating things the Trio ever did was when they altered the rate of Buffy's passage through time so, basically, she was almost a statue for all practical purposes while everyone around her was a blur to her. It was kind of sad that, when it wore off, nobody was there trying to help her since it happened in a park, I think. You'd think someone would wonder why this poor girl is barely moving and that maybe they should call an ambulance. Ironically, the episode seemed to brush it off as some sort of parlor trick when it would be fatal had the Trio been trying to kill her at the time.
Granted Strange would likely be unaffected though it would totally work on Stark.
Then you've got Jonathan's reality warping, as you said. It wouldn't work in the arena but, with prep and this being a scenario, he may well just create a world where Stark and Strange worship him. I'm not sure if MCU Strange has feats of shrugging off mind control.