I think Ben McAdoo was not brought here to create an offense that fits Eli Manning. I think he was chosen, because his system will make Ryan Nassib a star.
Just look at how the two have responded this pre season. To argue that Eli is better at this point is either making excuses for him, pointing to his past performances, or just being blinded by the homerness that comes with a guy that won us two titles. Meanwhile Nassib looks incredibly comfortable in the huddle, calling plays, and making plays... a lot of them.
I believe Eli has 2 years left on his deal, and he should retain the starters gig until that time is up... but, they will then have to decide between the two, and with McAdoo's offense in place, I think the writing is on the wall. And I think I'm ok with that.