I like the one-two punch of softening up a crowd with Evocation and then laying a compellable aspect on them with a (now greatly reduced complexity) Thaumaturgy ritual - whether that ritual is done normally or at Evo speed through Sponsored magic isn't so important to me at the moment. In this way it's a lot like the Mind Fog spell in the book.
In play, of course if the Warlock needs minions offscreen, he can just have them. I 1) wanted to double check such a thing was possible so as to have an excuse ready for "How did this bastard turn the whole town on us?" and 2) what it'd realistically take to do such a spell in combat. Having minions ready to go for the PCs is one thing. Being caught offguard and having to flee to somewhere there are crowds, trying to turn them into fodder to cover your escape on the fly? That's entirely different.... and it sounds like it'd be a lot easier to just give him Outsider magic or Kemmler-vision.
I also am okay with changing a High Aspect being done one-on-one. With that in mind, that options seems much more useful for people like the mayor, the town sheriff, and a threat to any PCs who might get captured by this guy. Sometimes those kind of changes to your character are a more terrifying threat than death.
As for using "throngs of people" as the flavor description for an attack or block evocation, I think that's cool. I think it'd be more like "the strip mall-goers suddenly reach out for you, grabbing at you and holding you back, then, just as suddenly, they relent and look around confused." Like the Warlock slapped 'em with a quick "Stop those guys!" directive but didn't make it stick.