Back in the early days KDF did not really have any content other than pvp. So you were mor ore less forced to pvp your way up to 50. That resulted in much more experience on the average KDF player.
These days things are different. But you still need a fed char first. Also there are less quests on the KDF side so you might still try to lvl a bit with pvp. While I don't think the difference is a big as it was I still have the feeling the average KDF player has more experience than the average fed.
Also there might be a disadvantage concerning ships. Now while the federation offers top escorts and sci ships it kind of lacks cruisers other than healers. The most popular ship from the shows is likely a cruiser, the enterprise.
Building a fed dmg cruiser is challenging. Most people don't want to be a healer or supporter. Most people don't even heal their teammates. So many feds sit in their cruiser, that can't support and can't do dmg and are pretty useless.
Now I sorry to hear that your enemys quit the arena. There should be a leaver penalty but I don't think there will ever be one. Most of the time I see feds quiting but there are black sheep everywhere.