I’m not a canon lawyer, but I think I can say with confidence that a bishop can be deposed by the Pope for any reason or no reason, and that there is no recourse.
The reason, though, is despicable. The Pope squashed the FFI, and has been punishing bishops around the world for taking in any former members. The Pope wants them starving in the gutter, or, at best, working at Starbuck’s.
This putative Pope has spent almost four years squashing people like bugs. He is utterly lawless, and a rank fraud. Someone recently wrote that his public persona—jolly, humble—is the phoniest thing about him.
I think that you may be right, but I suspect that there is a different way to go about doing it canonically. One way of retiring a Bishop is accepting a tenured resignation, and there are mechanisms for doing that. Saying that one has retired a bishop by using those mechanisms when crucial elements are absent seems, to me, not to work.