It's not letting the OC hire his own staff that's the problem or what makes it bizarre. If you hire an OC as a HC coming from the defensive side of the ball, that part is reasonable. But, if you're a 1st year head coach and therefore you know your big hype plan has raised expectations that hinge on the offense succeeding, you double back and check on the reasoning for every decision that can affect execution.
I run a fledgling technology startup company. I've got some programming/product/technical skills, but partnered with a far more experienced engineer because of the complex nature of the product we set out to build. If I let our CTO hire the next 5 engineers without verification they fit the culture or have the requisite resume, that **** is 100% on me. If I just let it ride blindly (don't know if that's true or not), I find that bizarre. Now, these coaches are million dollar salaried folks (as opposed to ****head startup guys at "lower" stakes) running a multi-million dollar program. You'd expect at least the same.