Don't forget about the number of guests who stay off property and buy tickets when they get there. As hard as it is for us on the Dis to imagine, there are many people who do not plan in advance. These guests cannot be quantified. The evidence also indicates they are not coming.
As much as Disney hoped MM+ would give them accurate and precise numbers, I think the evidence is to the contrary. Otherwise, park schedules and cast staffing would be set in stone. Yet they are more unpredictable than ever right now. ADRs merely suggest interest, as anyone can make them regardless of tickets. Even FP+ reservations aren't a guaranteed indicator of attendance to a particular park at a particular time. We humans don't function along set algorithms when touring wdw. Plans change last minute for a variety of reasons. The only data that still seems to actually matter is the number of bodies actually entering a park, which can't be known 100 percent until day of. Hence the frequency of early releases for cast as of late.
I firmly believe that MM+ exists for the most part to encourage guests to shop instead of queue for rides. It in theory increases sales and decreases demand on an already stressed infrastructure. It also eliminates the need for additional cast in much the same way as self check at the grocery store. This should be a win for guests, as Disney should theoretically be able to offer guests more with the savings, but guests are losing out too. Something is wrong when characters and entertainment are constantly being nixed. What that is, I don't know, but I think many of us can sense that there is a problem, as shadowy as it seems to be.
You are right in the sense that they were able to track resort guests and realize the numbers were down, hence the CM perks. None of which I was able to take advantage of, sadly.