I'm a little flabbergasted by the assumption that I don't let players play dominated/trapped characters.

In fact, we just had a great encounter where one of the players had Magic Jar cast on them. It was theatrical and a lot of fun.

That was a 6-on-1 fight, where Magic Jar was a way for the baddie to stay alive. It took a PC the players normally rely on off the battlefield for a moment, and was fun.

This is a 2-on-2 fight, two PCs versus to seriously hyped up, powerful characters. The Portent ability will take away some player agency; and I just don't want to take away more by tying it to the wrong spell.

This is near the end of a two year weekly campaign, and this is a fight that is supposed to be important, difficult, but winnable. There's a time and a place for being dominated, but this ain't it. Hence the request for other spells.