The number of players in Janus and Turnpike is always perfectly matched -- if, say, 65 of Faction 1 and 50 of Faction 2 get in, 15 people of Faction 1 will not make it into the battlefield and the battlefield will be 50v50.
That might be the intent, but it's not how it happens in game.
That may be the case for the offers, but not everyone accepts the offers, so RG are usually short by around 3-6 players by the time the match kicks off. I don't know why it is that RGs aren't taking their queues, but it happens consistently. Then when things turn against the RGs, a lot of people start AFKin, or leaving, enough so that most of the match RGs are down by around 10 players.
I really have no idea why Free Knights players take their queues but RG players don't.
The easiest fix I could think of would be to just not let people respawn if they die if their side outnumbers the opposition. Basically so that the side with the most players could only have a number of people alive equal to the total number for the smaller team (not the number the smaller team has alive). The larger team would still have an edge, and players on the larger team would still get to respawn fairly quickly, but it would at least be a little more balanced.