I would say this is another good example of coaching making a difference, imagine if the Falcons hired Shanahan instead of Quinn as HC in 2015. That would be a significant rewrite of recent football history. The Falcons failed Ryan long term by bringing in a defensive HC, even though they got close to winning it all in 2016.
I know many on this board agree you want an offensive HC, because if your offense is good under a defensive HC you won’t be able to keep your OC for long. Compared to an ideal HC-QB pairing, there is no equivalent pairing on defense. Assuming the offensive HC is competent, the HC and QB grow together, continuing to build on the foundation installed back in their first training camp together. Having some stability at the skill positions also plays a role, QB’s and receivers continue to develop a chemistry that can transcend the playbook at times.