My DPS keys that use assist/follow all work fine. The character won't RUN to the target, but I don't have a problem with them lagging that far behind. You sort of have to lead your followers onto the target a bit.

In anycase all my DPS keys are two step keys that activate when pressed or released.

Step 1 is assist
Step 2 is DPS abilities with follow last.

They will swing and then follow. Works very well. One thing that you may want to consider as a melee boxer especially if you run sentinels or marauders, run Predation or Transcendence. The movement speed buff makes a WORLD of difference in increasing on target uptime. So much so that I have pretty much dropped zen from my sentinels in PvP, and will drop it from my marauders now that I have predation for them.