Everyone already does both of these.... Every single group I've been in did this.

I believe it's a bug needed to be fixed.
And a bug on game design side.
For example, if the warrior is present, he'll charge you immediately (and mostly likely chain-charge your party). For clothiers, that means almost certainly 1 or 2-shot death.
If this is intended to be, then for certain combinations, this heroic instance would be undoable by lvl187-equipped parties, which is contradictory to what Blizz claimed about its purposes.
Therefore, I believe the fight should exactly be like what most people have been doing: separating mount phase and floor phase, bosses would not aggro immediately after mount phase.

Or, simply keep them clumped up as you are knocking them off their mounts in the previous phase, then have everyone but the tank get clear of that spot immediately after the dismount. As long as the tank is prepared with some defensive cooldowns to offset the initial burst they're going to take, there's no need to run out. I've tanked plenty of transitions using this method without losing a single group member, both regular and heroic.

This shouldn't be necessary. The tank should be in the middle of the action and intent on pulling ALL the aggro. Everyone else should be getting as far away from the 3 bosses as possible. If you pull one run to the tank so he can get the boss off you.

If you do this and still die your tank either isn't trying to get all 3 or your healer is asleep at the wheel.

Worst case 1 player dies but there's no excuse when so many classes can bubble, feign death, disappear, or simply run away really fast.

@ Urza: Not a tank or healer, are you?

Sorry, As a tankadin I have smacked all three with a HotR and the warrior still charged and one shot the priest. They keep aggro from when they are mounted, unless you have a taunt like challenging shout which forces them to hit you, you can't hold aggro. The amount of damage done while mounted is insane.

The transition is broken because it is a phase switch and has no aggro dump. Bad mechanic. Until they fix it, we just run out.

He targets the healer and if you happen to be a Priest you will very likely die. The transition is broken and he will still charge regardless of the tank. i have even had a Dk dg him across the room and he still charged and knock me into the wall. While I have seen some groups get through this phase without exiting it was only because he did not come and finish the job after the knock back. Now I just tell them to make a bee line for the door and will either make it out or spirit run back to the instance. I don't mind taking the bullet for the group because it is a short badge run, long into or not.