Chris, waiting until winter to do heavy thinning will just invigorate the tree. Right now and then once more around September would be the best time to spank this bad boy, taking as much as 1/3 off of it. If you do that and bend the remaining branches down, you will have a much different tree next spring. When you bend the branches down, you may end up with water shoots coming up from the apex if the arch; refer to the thread on Espalier Reworked to see how to deal with those Espalier Apple Trees Re-worked
I wouldn’t worry about fire blight; the risk is worth it, especially when you just said you’re considering pulling the whole thing out otherwise.