I think I agree with where Yareet is heading - Minty is more the exception than NEv.
There's a long history of players transitioning pretty successfully at coaching their own clubs, from the Leicester boot room through Exeter and the Saracens coaching factory (which, whatever else you think of the club, has produced a lot of very successful coaches). There are also a good number of counterexamples - think about how many of the coaches Leicester brought in from outside have lasted more than a season or two.
I think the issue was that Minty's personal style didn't make that transition easy within a Quins environment. It's hard to go from being the sardonic representative of old school rugby (and I'd be willing to bet someone who'd break the rules on occasion) as a player to the guy laying down the law in defence with the same bunch of players. His success with the other teams he's worked with suggests that he's a good coach, but he needs to be seen as a coach from day 1.
England would be a big step up, but in Borthwick he's got someone who knows him very well and has made a similar transition pretty successfully. I imagine it'd be a bit weird for Marler and Cole - but with DC now retired I am pretty sure they're the only remaining members of the England squad who knew Minty as a player.