This whole thing about is a coach good if his players or bad and vice versa is pretty dumb. A coach legitimately can't make a bad player good. They can only make players who are good enough to stay in the league better and can help rookies who belong in the league develop faster.
That being said Davante Adams could get the worst WR coach in the league next year and it simply wouldn't matter.
So when you inspect a guy like Engram you can say look at what he was working with as an excuse. Look no further than all those guys mentioned went on to either leave the league or play as WR5 for other teams. Engram gets a pass for his time as WR coach of the Ravens.
But he certainly does not get a pass for the Wisconsin offense he ran
davante adams is a good example of how a good coach can help a good player become a great player
After a couple of years where Adams was good but not elite, he spent time with "Dubb" in his offseasons working on specific parts of his game (releases especially) and he's now the most dangerous WR at the LoS in the game
we've seen "Dubb" do the same thing with releases with Hollywood and even Duvernay - helping them develop their footwork and hands and then also their hip sink at the breakpoint
but you're right though that, at this point, Adams doesnt necessarily need anymore good coaching, because he's already had it and it's not going to make him worse at this point
Engram's wisconsin offence shouldnt be held up as a great reference point to make him a viable candidate but also he doesnt need a "pass" - he dramatically improved that offence from what was there before (which is probably why he's getting these interviews) but that offence isnt particularly inspiring
i think the greatest way of finding out how you feel about a position coach, is what do they do when they've got key players missing in their group - James Urban with Tyler Huntley and Anthony Brown for example - we've seen Bobby Engram get guys like Eric Tomlinson to give us meaningful snaps but also should be noted that he couldnt do anything with Josh Oliver (but George Godsey did... who also got an OC interview with Harbs)
easiest way to see whether your position coach is any good:
1) how well do rookies and young players develop
2) how well do backups do
3) how well prepared/managed are new players coming into the team with limited prep time
4) are there obvious, group wide technical improvements