McD will reconfigure the offense to match the current abilities of players he has to work with -optimize their strengths and avoid exposing their weaknesses and vulnerabilities. He just recently said as much.
There are layers/levels of understanding the "complete offense" that new players need to assimilate in some sort of sequence. New players need to have the ability and the willingness to keep working at it relentlessly. However much progress they've made at a certain point in time, that's the extent of the complexity they'll be asked to execute - and then only to the limit of their general skill level.
The thing is that, although Hoyer has "experience in the system", he doesn't have anywhere near the level of understanding that Brady does, and his skill set is obviously different. If (God help us) Hoyer needs to take over for awhile, McD will alter the offense to optimize however much Hoyer can do well. McD isn't going to expect Hoyer to run "Brady's Offense" just to have him faceplant. That would be stupid.
The same thing would apply to Griffin, or to anyone else who becomes Brady's backup. They won't be running the "Brady Offense"; it'll be something different. While it seems unlikely that it would be as successful as Brady's Offense, it's not a given that it would be a complete disaster.
So, what it comes down to is objectively and dispassionately evaluating what strengths and weaknesses Griffin has versus Hoyer's strengths and weaknesses. Since neither of them would be running anything more than a limited version of the offense, it's a matter of figuring out which limited version - Griffin's or Hoyer's - would be most likely to succeed against the specific defenses that the Pats will face in the regular season in 2018.
