I'm a federal employee of a certain plumage. I'm inclined to agree that my wages are far higher than one might expect for a receiving clerk in the private sector, but I also have lots of duties related to my military obligation that I have to take care of M-F because there simply isn't enough time for it on drill weekends. So I consider it a wash.
As far as being fired for poor performance, I suppose it depends on how poor. Obviously I can be fired on the spot for something egregious; theft, threats of violence, refusing to do any work, etc. I can also be technically fired for three consecutive unexcused absences but this is very rarely enforced. But for poor performance in general, it would take a minimum of one year of me only hitting 75% or less of my performance standards. "Unsat" for the first six months, they'll wag their finger at me and if I'm due for a raise, I don't get it. Unsat for another six months, buh bye.
For something more nuanced, we do have a union, but membership is optional, so they're pretty darn low key as far as unions go.