There are currently 4 guys in the entire NFL that fit that criteria: Peyton, Brady, Rodgers and Brees.
Would those same guys have fit that criteria in Year 2? Nope! Possibly Manning, but he still had his share of problems still after Year 2. Brees was considered bust material after Year 2, so much so that they drafted a QB to replace him.
I think Tannehill has a higher ceiling than Schaub, and a guy like Kubiak would bring that out.
A better point I've kept trying to bring up is that Kubiak got significantly better production out of everybody he's ever coached on offense. Including John freaking Elway.
Elway threw for over 20 tds 6 times in 16 years. He threw for 22, 22, 25, 26, 26 and 27 tds in various years. Numbers in bold were the four years his offensive coordinator was Gary Kubiak. When he was 35-38 years old. Elway posted four of the five best passer rating numbers of his career (1995-1998). When his offensive coordinator was Gary Kubiak.
It's not about finding an OC who can make the QB look good. It's about finding the OC who will get the most out of the quarterback he's working with, regardless of whether that QB is a Hall of Famer (Elway) or a flat out scrub (Plummer).