i handle my casters and melee this way:
i have two seperate follow macros
one is for the casters and i have a key set for them to stop
the melee i dont have a key for them to stop follow as they will automatically do that when they attack a target.
i just have they follow keys set differently so i can make melee or casters follow me at any time seperately.

Seems to work so far, i've done a bunch of raids so far using this method.
nothing like merc but old school stuff