There's been no"fixes" because a latency-proof mudra and TCJ require much more work than changing a potency number somewhere in the gamefile.

One day perhaps they'll recode the way some actions are dealt with (player side instead of server side), but I don't even know if this can be done on a spell per spell basis.

This issue affect every job on different level and this is something SE is aware of but there's no easy fix. Heck I wouldn't be surprised if they'd basically have to recode the whole battle system to make it more fluid like any other MMO. (Someone will surely confirm / infirm this part)