They were using lighter balls in that FO and Isner is a servebot (one of the best ever) who can push anyone to a tiebreak on any surface. Falla has no real weapons but took first two sets against Fed at Wimbledon.
I don't see it as the same situation.
Nadal actually usually always deals with servebots quite well. You'll find his record against guys like Raonic, Karlovic, Isner etc is better than anyone's. So it is very similar, Isner may be one of the best servebots ever, but against Nadal who usually deals with servebots quite well and at RG of all places?
Fed just had a terrible start to that match, how else do you explain him bageling Falla in the 5th? Did his injury heal up? Usually when you're truly injured, it takes its toll the more you play... He then thumped the 16 seed in the 4th round, so I guess his injury disappeared? But then came back when he lost? Typical Fed logic of course... Berdych on his day was tough and he was no stranger to giving Fed some big problems at majors.
Let's just agree to disagree... I won't change your mind, you won't change mine. It doesn't even matter, like I said being the favourite or not is pointless. Rafa wasn't the favourite for US 13, 17 and 19 and still won them, whilst for AO11 (according to bookies) he was favourite - which shows how pointless it is.
If I were a betting man and Novak was allowed to play this AO, my money would be on him... but without him actually playing, you never know what could've happened. Fact is Nadal missed quite a few slams where he would've been a strong contender and given his record in majors, my money would be on him to take at least one of those with a good chance he'd snatch 2 of them. Again, can't say for sure about that either since that didn't actually happen either.
But if Novak fans want to claim this as his title even though he's not playing, good luck. It doesn't matter.