no, you still have the latency issue.

when you click on a new target, that information goes from wow1 up to the wow server... then down to you party members. this will take at least 2 * latency, or about 200ms on average... and remember, network latency is not fixed... it can fluctuate due to various network conditions

when you hit 'fire'.. it will go to your alts immediately, < 1ms (this won't fluctuate). if the information for your new target has not been received by your alts, then your alts would still be pointing at the old target... and would try to fire on that instead