An idea for the wave drop system.
Why not have the world segmented quarters, one for each faction. Then each faction spawns in their segment to start the BR mode. They slug it out until they have champions and are ushered towards the other faction areas. They then join in another wave but in another faction area now all geared up. There could be time limits to make the transition if that helps game play. Instead of a circle arena, make different points of interest the focal points to get too in each segment and essentially capture that area. The final factions standing try to take a holding point in which ever segment is closest to both and the winner is the person / team that is last standing at the point of interest.
I know there are lots of areas that could cause a few problems but I think if this was bottomed out it would make a unique experience within the game's lore and make a reason to pick certain factions. This could also be just free for all and not matter what faction you are to start with but zonal objectives that migrate to new zones is basically what I am getting at.