You're right, it isn't about a multiverse.EEAAA started off with some nice ideas but I was bored by the end. Too much relentless action for my tastes. And it didn't actually make a whole lot of sense. I can imagine whichever physicist they had as a consultant getting rather frustrated, and I felt like I'd been a bit misled by the end because it's not really about a multiverse at all.
It's about the life not lived. It's about regret and missed opportunities and existential angst. It's about cultural displacement and the impossible situation of being between what was and what is. It's about having children then losing them precisely because you gave them the freedom they now want to exercise.
It's about a lot of different things, but it isn't about a multiverse.