When I logged on this morning there were 30 in the arena and an ENY of 21. I have no issue with this( as I have the ability to die spectacularly in any vehicle), just out to understand and learn yet another aspect of this game. I can't recall the exact numbers per side though it wasn't overly different.
Do a screenshot next time
You probably just looked at pure player numbers and did see "only" somehwat like a 7 player difference between high and low country - Look a the percentages. Example:
Country A 13 players 43%
Coutnry B 11 players 37%
Coutnry C 6 players 20%
Doesn't look like much difference, until you realize that A is outnumbering C by more than 100%...
*modified after BaldEagl pointed out my error*