Well, to be frank, the idea doesn't sound very interesting to me. Yes, on a Turing machine, the universe would take a very long time to simulate. Perhaps our simulators are very patient, or perhaps they're using something more powerful than Turing machines.
It's possible I'm totally misunderstanding you, though. I know what Everett branching is, but not what the associated "factor" is, nor do I know what it would mean for one of these factors to dominate another.
Edit for typo.
As an analogy, imagine two bacteria. One of them represents a "sim" and one of them represents "reality". Every time a quantum branching - a effectively-irrevocable "collapsed wave function" - affects each, they reproduce, splitting into two or more Everett branches. (Also, every time one of the realities ends up containing a non-identical sim, you also have a new sim; but this is a trivial correction). My argument is that the "branching factor" or "rate of reproduction" of reality will be so massively bigg...
I've written a prior post about how I think that the Everett branching factor of reality dominates that of any plausible simulation, whether the latter is run on a Von Neumann machine, on a quantum machine, or on some hybrid; and thus the probability and utility weight that should be assigned to simulations in general is negligible. I also argued that the fact that we live in an apparently quantum-branching world could be construed as weak anthropic evidence for this idea. My prior post was down-modded into oblivion for reasons that are not relevant here (style, etc.) If I were to replace this text you're reading with a version of that idea which was more fully-argued, but still stylistically-neutral (unlike my prior post), would people be interested?