While I tried hard to use and enjoy Battle Regimes, I find their implementation rather convoluted and cumbersome. The level of steps required is too high, and in the end lag doesn't help.

I would suggest bringing back skillchains from FFXI.

Mind you, I'm not one of those that advocates turning FFXIV into FFXI-2, but when you make a sequel porting over certain staples of the previous game isn't a bad thing, is it?
I think skillchains are one of those staples.

Their usage and execution was much more intuitive and immediate than Battle Regimes, they didn't require additional cumbersome steps, and they simply were the best balance possible between fun, simplicity and complexity.