I tend to disagree on this point - it is so much more than merge doing their job right. Really is and I having spent months at BTM, I have seen dozens of reasons for a back up and have to tell you, with at least BTM in particular, you're very inaccurate. If grouper is not going as quickly as they should, leaving rows empty, it slows down the line. If dispatch or unload are taking their time, slowing down dispatch, allowing the other station to steal the dispatch or worse - both are going slowly, it'll be messed up. If exit is having trouble loading someone (ECV, disability, someone over the safety line), you cannot dispatch to send it. If you're bringing out another train, for a moment, you must hold your dispatch, waiting for a certain thing to happen. So, I could be at merge, being the best merge CM of all time, and if anyone of those things happened (which they did daily), doesn't matter. Backup and then offset number of people on fp makes it worse, compounding the backup.
Additionally, fastpass is designed to give out (depending on the setting so the number can fluctuate) 80% of the amount of guests we can handle that hour, allowing for 20% on standby. It is figured on guests we can handle per hour. So if, let's say we can handle 1000 people per hour for the hour of 10-11 am (just for a hypothetical number), so we give out 800 fastpasses. Let's say 400 of those people decided to come back at 5 pm. Well, now, 5 pm is trying to accomodate it's 1000 people, plus this additional 400. They give out FP to compacity (as a fact), so then additional people over that number WILL in fact cause a slow down on both lines, because to keep FP moving properly, you have to cut into the number of standby you can use. So, yes, even a merge guy is doing a perfect job, you can still be faced with a particularly rough line.
And you'd be shocked by the number of late FPs. Some days I would see them in a nearly even ratio - people whose fps were late, trying to get in early (everyone always has a great reason they're early and can't use it later) to people who can and should be on the line then. The fact remains, people coming late to FP is a courtesy, not something people should be flaunting in their faces, in my opinion. But until Disney says something, I guess we just have to accept how it is.
-Nicholas