I would try ditching the assist and change the dual conditionals from [harm] [target=targettarget,harm] to [@focustarget,harm][@targettarget,harm] and see if that helps speed it up. If that does make a difference then you may have to rethink your targetting style, assist has always felt slower to me.
At least changing to [harm,nodead] should reduce the stuck targetting a dead mob. We would have to see your main's macro to know what his problems are too, it could be a combination of the two sets.