No that's not a fair way to do it if you take info account the fact that the employee has to sign away not just their rights to sue, but their right to full unemployment benefits.

He's not actually firing people, he's pressuring and bribing them into resigning voluntarily.

It's basically a nasty way of breaking the social contract of the employer - employee relationship, shifting what should be the entrepreneurial risk of the employer to the employee, without any upside for the latter.

I take back what I said about the legality however: it's fully legal and very common in the EU, it just isn't firing people.

I've seen it used in practice. There's nothing nice about it, and almost always the result of bad hiring. Only employees that wanted to get out anyway or are easily intimidated go along with it. And it can seriously bite you in the ass if the employee tells you to shove it and forces you to take it to court instead. (Because they don't really need to sue, any firing after that conversation will be illegal.)