“It’s also oxymoronic in the sense that the universe is everything that exists, which means that “multiverses” are part of our universe.”
Well, you can define the universe as everything that exists, which by definition rules out any multiverse. Or you can define the universe as everything that it is possible for use to observe. In that case, we can never observe any evidence for the multiverse so it’s a scientific dead end.
I think the dark matter/dark energy are just cosmic “fudge factors” to plug deficiencies in the current theories, but the multiverse stuff is just philosophy being done by people who are unqualified to do philosophy, because they’ve hit a brick wall that science can never penetrate. Really they should be leaving the philosophy to philosophers, but many people seem to have adopted the notion that science is the only legitimate means to reliable knowledge, so they do not want to admit that there are questions science can never answer, and have resorted to this pseudophilosophy in an attempt to pretend that science can answer such questions.
And one day in the not too distant future, you'll see that it is MUCH WORSE than any of the so called genius experts would imagine