I currently play with the "target=arena1 and so on" it works very well and you can use this to gib a rogue very easily as you do not have to target anything to kill all the arena targets.
The problem with this is that sometimes depending on your toons spacing or location when the gates open you may or may not get the same arena target order for each toon.
If that happens your toons will not target the same arena targets. So you will still need a focus setup.