This is one of those arguments that probly can't be settle for quite a while now. HT is still working on CT, plus finishing up the P-39 and La's, and has many more things to do probly. I don't think he has time to worry about people afk in tower for 2 hours, or arena caps right now.
Without the booting thing there will be people that go afk in tower beause they may have something that they have to do back in reality. Go pick the kids up at school for a dentist appointment, or maybe they're going to eat dinner. While they're afk the arena can be maxed out at 320/320, and someone just "has" to play on that arena but now can't (atleast until someone else leaves the arena).
With the booting thing someone has to go AFK, but doesn't want to get kicked for fear of not being avle to get back into the arena for a whole 5 minutes! So, they'll up a gv or plane at a back field and just sit there until they return. OR, maybe they go afk while still in tower and get kicked and can't get back into that arena. Now they'll come to the BB and whine about getting booted while eating dinner or some other thing.
I really don't see any way this can be resolved other than go to another arena for a few minutes.
My $0.02