I think a nice solution would be to lower reward amounts, if paid with mileage solely earned from flying. This would directly reward loyalty for flying an airline, without diminishing the value of actually using an airline to obtain miles, rather than a credit-card.

This would require differentiating between CC miles and flown RDMs (adding a layer of complexity to existing systems). Flights paid for with CC points could continue to be redeemed at the now-inflated points levels. Flights paid for with "real" EQMs could be redeemable at the more reasonable levels prevailing a few years back.

Not that this will happen, ever. It's nice to dream, though.