That's got nothing to do with anything, there isn't some curse on good managers doing poorly here because it happened a couple of times under wildly different circumstances two decades ago.
Critchely jumped ship to be assistant at a Premier League club just like Mapp, except he left a club in the Championship to do it. McCann left Doncaster in pre season at almost exactly the time Mapp left us after a phone call from Hull. Good managers will get poached and most are ambitious and will move. It's a far better situation to be in than no one wanting your manager (or players too, in our case. Cheers Karl). What you're worried about with Mapp the two you're advocating have been guilty of far more recently.
All this being said, and I also voted for Mapp, I agree that I'd be happy with McCann here too, he'd be second choice for me I think assuming Buckingham is out of the equation. Young manager, plays good football and has won this division before as well as getting Doncaster into the playoffs with what I assume was a smaller budget than we have relative to the rest of the league. Had Hull just short of the playoffs before they sold Bowen and Grosicki and nose dived. If he's in the home dugout against Derby I won't be upset.