Seems to me you're reading in worry into a statement that clearly shows no worry.
I don't think that is Dan saying he's "partial" to playing calling head coaches. Reads to me that he is one himself and he has a lot of appreciation for the the head coaches who are also great play callers. Appreciation for doesn't automatically mean preference for.
Seems to be that TCUDan is saying that a special teams coordinator can be a good head coach and head coaches who don't call plays can have an advantage when it comes to emphasizing the attention to details.
Seems to mean that TCUDan is saying that head coaches have other traits that are more important to winning games, than their play calling ability.
I don't get that at all from what TCUDan said. He seems to be saying that being a good playcaller or previous OC or DC are not necessary for someone to be a good head coach. You seem to be misintepreting him having appreciation with having a prefernce for.
To me, TCUDan clearly said he doesn't think that's very important.
I never said TCUDan said Rizzi should be the HC. TCUDan didn't say that Rizzi shouldn't be the head coach either, because you didn't ask him if Rizzi should be the head coach or not.