It’s more than this though; I describe it as the mathematics of democracy. With no actual examples, then we have to imagine some. A country as populated as USA, for example, is better served as a federation than as a unitary state with PR. But the opposite is true, when we imagine a small population like Ireland – then democracy is obviously better served with PR than as a federation of regions.
So there is a clear scale here and where would UK fit on it? Well, let’s imagine again; would it be better for Scottish voters to not have any devolved government at all and follow the politics of a Westminster parliament elected with PR? With, say, a 5% threshold for parties to gain representation, would SNP even make it to Westminster? It’s clear that UK’s population is too large for the simple implementation of PR. We need regional devolution to enable it.