OK maybe this is a better solution

remove cap
and change it so beating the banish in 5 mins is required to open the next one.
and set it so you have to complete a banish is 45 minutes to keep it
and add in more banish levels. so we have
10m
50m
100m
200m
500m
750m
1.25b
2.5b
4b
6b
etc

Then reset all servers to 10m banish.

This will slow down coin growth - while allowing large population servers to keep growing