it should be higher for an RX570, which driver do you have? Use the Aug23 Blockchain driver or get the new Adrenalin and switch to "Compute" mode in the AMD global settings...
Tried the latest driver - had 24.9 at best (compute mode)
Re-installed the Aug23 Blockchain driver - running at 25.3 Mh/s
Now I wonder if I can get any better at all.
Planning to try some new BIOS mods (haven't seen any appropriate though except Anoraks)