The hotspots aren't even that relevant. You can drop out at any point in a ring and still make absurd amounts of credits from mother lodes even though they are rarer. Of course rings are huge structures of many times the surface of the Earth, so depletion shouldn't even be a big deal...
Those magic minerals need to be devalued drastically, there is no way around it. They shouldn't be much more valuable than painate or diamonds. Sub-surface mining could be made more profitable for larger ships by drastically increasing the number of chunks released from a rock instead of rasing their market values.
If FD is preparing us for carriers, magic minerals is a dysfunctional way of spreading more money. Actually this is a non-argument, because player wealth can be balanced much easier by amending asset prizes. The amount of time needed to get to carriers can be controlled better by simply prizing them sensibly.
Other factors that could be used to balance this shlt are for example higher insurance costs and higher fuel costs.
This is a terrible idea. If you don't want to have a high credit balance, then mine less or jettison cargo. Let those of us who enjoy having a lot of money continue to do so.
Other people making a lot of money has literally no in-game effect on you whatsoever.