Top players will not move to England, why would they unless they get double what they get in the NRL.
It would be like Ronaldo moving to the Australian Hyundai A League.
The English game has not attracted top shelf Australians for two decades without paying massive overs for them.
Only a couple come to mind, Buderus and King.
Others have moved because they had been blackballed in the NRL like Carney and have come for a well paid Holiday.

I'm sorry are you suggesting that RL clubs should introduce some sort of scrip/truck system for paying players so the don't spend it on things you believe unacceptable?

They'll pay tax over here, buy food and consumer goods, they'll basically contribute to the Uk economy because they'll be living here. Not sure what relevance this has specifically to money in the game, as has been said no is donating their salary into the game they are just using it to live their life, whether from workington or timbucktoo. Do you give half your salary to our employer for investment?

Am I missing something?

The one ex international player I've talked to about their time in England said that their family took the chance to do the tourist thing all through England and Europe, and they ended up spending more money than they earnt. Not that they were complaining. They said it was a great experience for the whole family.
I suspect the exchange rate isn't that big a thing for older players, who are more looking for a paid holiday than to make themselves rich - because they are rich already.

The pound will shoot up approx 2 years after Brexit as other countries leave

Thats right and some clubs need to do more to produce better junior players.
The quality of the avergge overseas player is no better than the average Super League player we have in the country.