I feel like regardless of any kind of changes you make, Granary will still suffer from a lot of the same problems it has. The biggest one for me is that it's the most unforgiving map to lose mid on. I don't think you can possibly do anything about that without it being considered a totally different map at that point. You have to be so committed to mid (basically not stuck in the back-left corner or garage/ramp), as you will typically lose to a team who becomes committed if you're not.
If your team isn't totally committed (this typically includes the medic), it's easier to exit the mid and hold yard, but it's much harder to win the mid when you're passively stuck in a corner where all of you take the same damage.
If your team is totally committed, it's much more difficult to exit if things aren't going great (especially the medic, who has to make quite a long run out of mid and out of yard). Basically, it's common to have all six of your teammates die if you lose mid. You might have one or two get out if they are quick about it. Perhaps you might have a 3-5 get out if a very early call is made and everyone is in a decent exit position. Still, it sucks.
Which yeah, if your team is totally committed on any map, it'll be hard for people to get out, but Granary is a map where you cannot sit all the way back and do nothing. You'll get spammed to death and eventually lose to the other team collapsing on you. It doesn't play out that way 100% of the time, but it happens much more on Granary than any other map. The rest of Granary is alright but not that great.
I don't think Granary is a horrible map, but I would say it's the worst in the rotation.