It seems weird arguing about the value of a coach with someone who has Bill Parcels as his sig pic...
This made me laugh.
As regards the OP, it's a combination. Teams that suck have players who suck. Coaches can only mitigate the suck. So far, all the talk about players over scheme in the offseason can be written off as nonsense. They're wedded to their scheme despite not having the players for it in the front 7.
I'm starting to think this season is a tryout for next year. The coaches are seeing who fits what they want to do. McCarthy talked in the offseason about wanting to find pass rushers because, "they're going to score a lot of points," being, "in those type of games." It's like he knew the defense was going to be bad.
For all the focus on the secondary (which sucks), I think the majority of the
confusion we're seeing is in the front 7. The two gappers are catching their blocks instead of attacking and controlling the LoS. The OLBs are losing contain. The ILBs are rarely in a position to get downhill, making tackles 4-5 yards back if not further. That's just the running game.
I guess I'd argue the coaches rolling with the new scheme and not reverting to something the players can do better is on them. But that's part of their plan. This can be expected when schemes are overhauled and players who were just ok in an easier scheme are stuck with even more responsibility in the new one.