Even in that case, I don't see Maelstrom as a "major" attraction. My impression is that MK probably has four or five "major" attractions, and the others probably three each. Yes, this is subjective.
this is not to say that the "lesser" attractions aren't someone's favorite, and that their impact on park capacity isn't important, but I would have to stretch pretty hard to remember a time when a single park had multiple headliners, as I'm thinking of them, closed at the same time.
Another thing to consider in attraction refurbs is the particular tasks that have to be done. It isn't just about whether an attraction has water or not, but who are the people doing the work. "workers" and hardware aren't just generically interchangeable from job to job, they have particular skill sets that have to be managed and spread out across the array of tasks to be accomplished.
If the SM rehab that almost always happens in January was moved this year, someone had to have a reason for doing it.