"Those 10% of remaining miners would be making 10x as much money in block rewards as they were previously (assuming the fork in question doesn’t change the block reward), so they would be doing quite well for themselves"

You assume a constant ETH/XXX fiat currency rate - which given the incredible amount of popular press this would receive, is highly unlikely. You should at least footnote the fact that "money" means ETH, which, as you have argued elsewhere, ETH isnt currency, so then you should clarify exactly what you mean by "money" and those underly assumptions.

I think you should also comment on the real world ETH/XXX fx rate impact that a hard fork will have,