The problem with these announcer types moving in as head coaches is they're not used to grinding massive hours to make players better like the guys who make their bones coming up through the pipeline. So how are they expected to attract a top staff who is going to do that and produce the product you need on the field.
To some extent this affects the college coaches the same way. You gotta be real good to make that jump. There are a lot of good coaches in college, too, and I think the value of it is guys who would be stuck slogging as position coaches and coordinators for more years get to jump up quicker to running the show and their own staff. But the drawback is how good are you at your actual craft if you cut out some of those years of doing the work.
That same effect is there in any industry too, to a greater or lesser extent. In the military guys who advance too quickly end up being suits who lack technical ability. The ones who advance too slowly are often the best techically but boy they can get weird and tend to lack leadership skills. So for myself at least I want a guy who has done the work and shown effectiveness at each level.
Which means you can see the product on the field due to his positional coaching. I don't care how much the HC likes the guy. How does his position group respond in actual production you can see on film. Brown is a great example of this effect. Everyone loves him but his work on the actual field has never been impressive in the NFL. And with Coordinators in particular if you can't hold down one side of the ball you are not good enough. Because in the NFL you have to be able to function as the expert in-house for one side of the ball while also running the show and teaching/managing your staff.
Jeff Fisher is a great example of this too. Looking at his career I think he jumped too quickly. If he had been force to slog through more years as a secondary, LB, and maybe even DL coach before he made that jump to DC it would have benefitted him IMO. Granted everyone's different and all that, but I think the NFL has a problem with guys moving up too fast and what you lose is knowledge of details for each room they don't get to run.
One additional note is Morris. He jumped too quick I think in his first shot at HC. Since that time unlike Fish he had to eat some humble pie by dipping back down to work his way back up. Which benefits him. He has the leadership down as a result. Of course I know someone will list McVay, to which I can only say there are always outliers and he is a rarity.