It’s not like his goal was to reach them how to be a head coach.
You can be good at your role without being fit to be a head coach. Sure, a lot of transferable skills between an OC or DC and a head coach. Some roles held by an OC in one team will be done by a head coach at another.
But just because they worked under Bill Belichick does not mean they should be a good head coach. If anything, from what we know about Bill Belichick, it might make more sense for them to not be. Regardless, I don’t get the point of this take other than it being a fun fAct
Honestly it’s just fun to beat up on him