If they capped AoE in frontlines, its possible that everyone would be harder to kill. Almost every match would end in a time out and feel like Borderlands since the path to victory would be skewed toward completing PvE objectives (since nobody is dying). Either the team sizes need to shrink, or the map size/mount speed needs to be adjusted so that its harder to get all 24 players in the same location at all points of the game. I think that would increase the amount of 8v8v8 fights around the map and reduce the amount of 24v24v24 fights per game, and by proxy reduce the amount of AoE damage and permanent crowdcontrol chains while still keeping a balance of players being killable.

Changes like these might make Frontlines even harder for the casual "here for the xp/let 'em fight" player though, since smaller team fights mean the individual players action matters a little bit more. So not sure how they would feel about implementing anything like this considering the trend of the development team seems to be trying to dumb the gameplay down enough for everyone to enjoy. They did remove 8v8v8 frontlines for this reason in the past (pre-made teams brought more skilled players into a mode that was meant to be casual).