Rival Wings is the 1v1 style of content they should be focusing on expanding. Frontlines if you asked me is a lost cause for as long as the casuals have zero incentives to put effort into their games.

Battlegrounds is frequently compared to Frontlines, but its more similar to Rival Wings. It forces teams to split into offensive, and defensive roles. The only reason Rival Wings stays dead is there is no rewards for queuing into it. It's missing 2 key elements. #1, Incentive to play it, #2, Incentive to perform well so people don't throw matches for quicker rewards. This goes for pretty much any PvP mode, on any game ever. Fortunately there are many competitors who have trialed and errored many ideas, and when in doubt SE can just simply draw inspiration from them, in the rare occasion they've decided to invest money into adding replayable content to their game.

You can add thresholds to give extra rewards to the top 5 performers on either teams, or you can just reduce the rewards for people who are obviously playing lethargically and didn't press more than 5 of their spells in one match.