Quinn's back is probably not an issue of his stance. It's more an issue of the angles he's had to rush from and how he must take on behemoth Olinemen.
As a DE, he has to bend really hard to get around the LT on his rush. And he must take a LT head on often.
From the OLB position, due to the angle, he is not bending but is racing a LT to a spot, and often a TE is blocking him instead of an LT.
So I think Quinn's back will fare much better as an OLB; and he certainly has the athleticism to play the spot. There will be a learning curve of course.