This was not an issue of whether or not Rex was good.
I don't think you understand what it takes to get someone ready to play QB in FBS football. Do you actually think Morgan is ready now? Do you think he'll be ready for our next game? When we play Louisville, he will likely have nearly as many practice reps as he would have had he taken all of the first team practice reps that Devito had in the preseason, maybe more. Yet, he will still not actually be ready. He may be a better. He may be the same. He may look worse since BC had one of the worst pass rushes we'll see this season (at least that's what I read).
How quickly do you think a staff can evaluate brand new players while prepping for a season in an abbreviated off season? How does a new OC evaluate veterans he has never worked with in the absence of spring practice? There is limited practice time and no crystal ball. Any reps you take from the guys on the two deep to evaluate unknowns are reps you can't get back. A staff goes into the season hoping their first team QB will make it through the season and probably knows it will be rough, if he doesn't.
When you reference freshman QBs getting playing time for other teams, how many of them were 1) elite prospects 2) unexpectedly forced into action or 3) able to enroll in january and go through a full spring and summer?