You would have 150/100 people in arena 1, and the other would have 10 or less and you would be stuck locked out for an hour or two. The boot idea was all snailman's fault but it did alleviate a BIG problem for the Euro guys, it has just moved it 4 hours later with a similar issue but not as bad. You have two arenas that both fill up within 10-15 minutes.
A few comments from the Snailman

Towards the end of the old system with caps just kicking in, we were up to 3-4 hours for the second arena to get up to numbers. If it had been "only" one-two hours, I would not had proposed the boot mechanism, it would clearly had not been worth it then.
Since the on/off peak arena system has been installed, the number of players online continued to decline. That means the time it takes for the second LW arena to get to numbers starts to increase again. In effect, the "US players" start to experience the same problem as the "Euro guys" did. It just is not nearly as much pronounced as it had been. It still sucks, and to be honest, I do not see it getting any better. The lower the absolute number of players online is, the more difficult it is to create two balanced late war arenas.