Yes mages have the wrong recovery delay but dexxers (specially archers) have the advantage over a bug related to swing during turns so they can shoot while chasing people between trees, walls, etc.
Something in my opinion that would balance a little bit, because nowadays 99% of the mages rely on weapons with mortal strike to play, is the
Enchanted Apple which is pretty simple to code.
If I get some extra time I'll check OSI for mage spell delay discrepancies using UOSteam, but it would be better if someone with low/stable ping test it, I can provide some macros for testing that will output spell delays. Demise already took the very first step which was fixing the target exploit bug.
PS: I've reported the dexxers swing issue previously (years ago) including a fix, but it never got in because casting is also broken.