You make an astute point that these coaches can develop defensive players. But your point also contains an implied point regarding development time and growing pains.
I would say McLeod developed into a top performer in 2015 which was his fourth year with the team and third year starting. As you point out, he had some rough moments in 2013 and 2014.
So if the McLeod path is followed as you suggest, then we probably shouldn’t have confidence right now. That confidence will come a few years down the road after Mo develops some after getting live experience. If we’re accepting that Mo needs to develop but the coaches can do that, as it stands right now, we’re still taking a step back. IMO, that’s cause for concern.
Personally for me, it’s not only about the coaching either. It’s also about the players skillset. McLeod came into the league with a coverage skillset. And you have pointed out in the past that he often played nickel CB. Alexander lacks that skillset. Can coaching create a skillset in a player?