I like this plot. No one else will.

From the first time I heard of Mission Architect, I thought a really cool plot idea would be for the player to be completely outclassed by the mobs (say they're all lieutannants and bosses). Their goal is not to try to beat them all, but to free a captive Hero (that is, a friendly AV) who merrily mops up the bad guys because HE outclasses THEM.

Although I like watching NPCs beat each other up, I realize that MA players may not like this as much. For one, the big AV will kill-steal a lot of their rewards away. Also, if releasing the AV triggers "Mission Completed", then the rest of the fighting is optional and kind of anticlimatic. On the other hand, if the final goal is to mop up the villains, that requires this to be a "Defeat All", and a lot of players don't like those.

Is there a way to keep my premise and still make it fun to play?

What if the end goal is a clickie or destructible object, and the AV only fights defensively? Then you use him to protect you from the millions of mobs, or just give him defensive/crowd-control powers. No kill stealing, and no defeat-all. Is that good?

Few players want to be spear-carriers in someone else's story, especially if that someone is presented as much more powerful and/or cool than they are. (One of the primary offenses of the official villain content is that you spend most of your time being a lackey to others.)

In other words, your subject line may be quite accurate.

Story-oriented players won't touch it with a ten-foot pole because of the reasons Joule mentioned, and rewards-oriented players won't touch it with a ten-foot pole because the hero will be taking all their rewards. Both types of players are better served with the final mission of the "A Hero's Hero" arc, where you free Statesman and he'll basically clear the map for you, which gives full rewards since it's a dev-created mission.

Seems like OP already knows "no one" will like this plot. I'd still say go for it - if you enjoy playing it, you've done good. If someone else down the line plays it and the story drags them in to the point where it works for them too (which any story should do, really), even better; if not, big deal.

Oh, as to your your premise - you can make that just one mish of say four, that should leaven the chagrin of some players a bit.

Agreed with others here, this idea is likely to be received poorly. You might find people who judge it on its pure storytelling merits, but you're going to get a chunk of people who don't like the story, no matter how well told, and a chunk of people who will be turned off by the AV taking their reward. Then again, people looking for reward may not be in AE much anyway.