A deist creator explanation is equally untestable, but is probably less parsimonious than a multiverse explanation.
The definition has "unwilling to spend money or use resources; stingy or frugal" but I'm not sure what you're describing as less frugal. Is it a way of saying the deist explanation is more likely?
If a multiverse theory could give a way to get a universe out of nothing, it would be a lot more elegant than a deity theory. The deity theory after all is incomplete, it just supposes that our universe is embedded inside some sort of "outer" universe where deities live, but that outer universe also has to be created somehow.
I want to reiterate that I think the side you are arguing for is ultimately the "right" one, but I'm not sure I buy this argument.
Sometimes parsimony is having a fundamental thing that other things "reduce" to, that other things are explained in terms of. Someone intent on adding a deity can insist that it's not merely one extra thing among a dozen things. Instead, it is the one fundamental thing that gives rise to the dozen things. And therefore is more parsimonous.
I wonder if the right thing to do here is bite the bullet and admit that, yes, such a thing would be simpler, but you merely think you have a simpler thing when really you have smoke and mirrors.
Adding a deity to the explanation requires adding an "entity" completely nonexistent in the current models that are the basis for the multiverse, i.e. those within quantum theory and cosmology.
I think the deist can insist "My explanation is the most parsimonous. I have just the one thing, a deity. You have a kludge of a dozen different forces and laws and variables."
The "parsimony", the "simplicity", the unit in which we count entities - is that of Kolmogorov complexity. "A dozen different forces and laws and variables" is significantly simpler, Kolmogorov-wise, than a thinking entity. There is orders of magnitude less things to specify about the former than about the latter for a complete description.
The root of my question is I am uninformed of anything with quantum theory or cosmology that makes a multiverse more likely than deism. Do you have specific examples from quantum theory or cosmology that makes a multiverse more likely?
Neuton's laws of gravitation/motion can explain why a ball travels in an arch, why the moon rotates around the sun and why an apple fell on his head. It's frugal in the sense that a dutch oven is frugal. You can use it to make pie, bread, soup...
>Since neither has any explanatory power that is not already contained in the phenomena they are offered to explain,
That is what these different explanations have in common, for sure. However, you seem to be defining that as parsimony. But there may be a lot of different explanations that are equally wrong, that differ in how complex they are, and those differences are differences in parsimony.
No, it's just, essentially, the numerator of parsimony; the denominator is the complexity added to the model; but a zero numerator makes consideration of the denominator irrelevant. (Normally, you compare parsimony of explanations with non-zero explanatory power, so the denominator matters a lot.)