It certainly can be. However, if it's a 'golden handcuffs' situation a 'guaranteed' vest of several million dollars for a 3-5 year commitment is something that I would certainly be willing to take.
I think that's the point. Sometimes the acquiring company is hoping you'll get bored or fed up and walk out before you can vest. Why would they keep you productive which only serves to sustain your incentive to earn a couple million, when they can instead pay only a salary and hope you give up before your years are up?
I hate the definition of "acquihiring", which seems to have been written by a PR firm. It's made out to sound like an altruistic process that magically overrides the business's normal strategy where all that matters is the bottom line and bowing to investors / board members. The reality is that when acquihired, you've entered a new company with its own culture, underhanded and ruthless politics, and ulterior motives.
There is very little truly irreplaceable talent worth paying millions for. What an acquihire is really saying is "We need your help to transition this product into our company's structure. We can't do this in only 2 weeks, so we'll say now that you will be with us for years. Secretly we hope you leave shortly after the difficult transition is completed, but before we have to pay you".
If any business out there acquihires to the spirit of the definition, thanks for being of a rare species.