I failed to mention one major additional point. Decoherence and MWI also account for the observed fine-tuning of the universe to support life, including key details of the inflation hypothesis. The standard interpretation doesn't.
As to conservation of mass-energy, this seems to be something that conflicts with your intuition that if there were decoherence, mass-energy would be divided up into the various branches and thus diminished in each branch. If you did accept the superiority of decoherence & MWI over the standard interpretation, you'd have to set this intuition aside.
You are free to select the version of Occam's Razor that appeals to you. I like the one that chooses a complete explanation (that also explains fine-tuning) over an incomplete explanation that also requires an exogenous wave-collapse for the first natural observer.
How many universes "branch off" from a "quantum event", and in how many of them is the cat dead vs alive, and what about non-50/50 scenarios, and please answer so that a physics dummy can maybe kind of understand?
(Is it just 1 with the live cat and 1 with the dead one?)