It doesn't, not necessarily. But you need to check your history. Howe did leave Bournemouth, flopped, and came back home to you with, frankly, his tale between his legs. Not denying he has been successful with Bournemouth since - but some managers (like some players) only 'fit' one club, and aren't nearly so hot elsewhere. Graham Taylor - genius at Watford; apart from that? Bobby Robson at Newcastle (OK he was better for England than some), Alan Mullery at Brighton (first time round) - there are plenty more too. And don't forget, Bill Shankly was a not very successful lower-league journeyman manager until he ramped up at Liverpool!
Just enjoy your time in the PL while it lasts (and you know as well as I do that all smaller clubs (those outside the top seven) will eventually slip up and have that 'bad season' and be back in the lower leagues before they can say 'Boo') and please don't feel the need to sneer at Hughton's considerable achievements.
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