I suspect that large maps made a lot more sense when LW was a single arena.
IMHO they still worked after the spilt, and i was actually glad when they came back. It's only in the recent two years that numbers went below whatever the critical point is. Not too long ago the lowest offpeak population was about 100, and that for a short time only.
Last year it went down to about 50, and we are for many hours now below 100. Same was true for the old caps mechanism. Years ago we had about 1 hour downtime when the caps kicked in, before both LW arenas finally were balanced. Last year we were approach in 4 hours downtime, severly crippling the game for those trying to play at that times.
What my stats unfortunately can't show (and thus I can't prove) is my strong impression that offpeak population has declined much more than (US) primetime population.