Hiring entire teams together is risky. It can be difficult enough to integrate individual hires into the company’s way of operating, especially when companies grow quickly. A team that has already worked together can have a lot of resistance to changing their ways or integrating into the rest of the company’s way of operating.
I’ve been at companies that tried this in the past. The teams that came in together wanted to isolate themselves and operate independently, and they had little interest in changing anything or adopting the same tools that everyone else used (one team tried to refuse to adopt git because they all used and liked subversion).
Usually these teams were laid off together. A team that quit en masse because their employer wouldn’t cave to their demands would be even worse for trying to integrate with the company. You don’t want to bring in a group of people who tries to be the tail that wags the dog and will quit en masse again the next time the company doesn’t give in to their demands.
If you're spinning up a new project/org/whatever hiring all the expertise in a single shot is so much more efficient than one-by-one. If they have agency, it's often a recipe for success.
I don’t think “we held our previous employer to ransom” is the sales pitch I’d go with.
Deception aside, this seems like a reasonable idea, and I've wondered if anyone might do this as a result of covid (as in, "we quit en masse when our employer wouldn't let us stay remote, wanna hire us?"). A mature team that's already worked together and gone through norming-storming-performing sounds like they'd be better than 5 freelancers thrown together.