Mate, are you smoking the whackky baccy? How you could you pay an SO2 Reservist £500/day and then let them work 8 days a month and take home the same as a Regular does for working 22 days a month? There would be a riot!
I think you are trying to compare VERR and ADC to contract consultancy in the commercial sector - it isn’t the same. The whole idea is to offer roles/posts out to those that still want to serve, with a much reduced commitment, for a symbiotic relationship between the Service and the part-time retired workforce. If you want £500/day or much more then come knocking via the various outsourced contracts in MOD working for the likes of PWC, EY, KPMG, et al. They get paid those sorts of consultancy fees for fixed term projects/programmes.
Finally, as in commercial land, if you don’t like the rate that VERR/ADC pays then don’t do it...