Why transact via cryptocurrencies instead of other systems? Because of these other desirable properties. They're the value cryptocurrencies add to the world and the reason why people choose to them despite the inefficiency. People transact in Ethereum because they want to run smart contracts. People transact in Monero because they want privacy.
> So it absolutely makes perfect sense to measure how efficient these systems are processing transactions, and the way to measure that is by looking at how much it costs to process a transaction with each of these systems.
I don't think so. People measure this in order to compare with traditional banking systems which are centralized, require trust in institutions and affords no privacy. This is not a fair comparison.
This is a big assumption, and almost certainly untrue.
That's an ok general rule, but it breaks down in a lot of circumstances. Look at scams, for example. People pay quite a lot for them, but at a societal level, they have strong negative value.
If you wanted to know how much people are willing to pay for decentralisation, trustlessness and privacy (most certainly not an infinite amount of money) you could also do that, but that's answering a different question.