Sources: Dennis Allen’s recent mishandling of Kendre Miller’s injury created internal frustration, Miller currently healthy but can’t play

The reason ML is still saying that DA is a great coach is because its what he believes is true. Notice, he didnt say that DA was the best HEAD coach, only coach. And Its true many around the league think DA is a great coach (DC). I think ML was also accounting for DA's 16 or so year tenure as a DC in his sweeping statement. Occam's Razor would suggest this instead of some narcissistic conspiracy theory.
I concur, and by all accounts DA is a great "coach" just not a great HC.