This is of course not including the yearly Unity subscription, where Unity Pro costs $2,040 per seat (although they may have Enterprise pricing)
Absolutely ridiculous. Many Unity devs are saying they're switching engines on social media.
Up until now companies have been getting away with this because of "user agreements." Nobody has had the money and interest to get them in court.
I don't see any possible way this survives a lawsuit, for exactly the reason you said. This is almost certainly not legal but nobody has had a reason to get precedent to say it until now.