...how would you characterise dominate person cast with indefinite duration?..

...upcasting dominate person at eighth level can maintain up to eight hours with concentration, so i'd be inclined to consider twenty-four hours duration equivalent to a ninth-level spell, but perhaps i'm under-gauging the difference in power between eighth and ninth-level spells?..

...regardless, in this particular case it was cast with indefinite duration plus disadvantage on the saving throw against a hostile player character, which i'd like to translate into mechanical terms: maybe a ninth-level casting with heightened metamagic plus silvery barbs?..

...i'm playing with a DM who has a poor grasp of fifth-edition's mechanical balance and i'd like to help him understand just how adversarial his homebrew and houserule tendencies are leaning, especially for early tier-two gameplay...