Keyword: Viable

Rival Wings exists, but it is not in the roulette, making it unviable compared to Frontlines for a pickup and go style of play (this could be fixed it was added to the roulette).

We could use a large scale 1-Team vs 1-Team map (16 vs 16) with a simple yet effective mode like Capture the flag (CTF) or something similar. Something that allows for strategy instead of dealing with scenarios outside your team's control, such as hoping certain nodes don't pop all at once in a corner of the map for one team while another team opts to focus yours down, thus allowing the unbothered team to just farm.

So why add a new mode or add Rival Wings to the roulette?

Strategic Competition: Large-scale 1 on 1 Team PvP modes allow for more strategy and as a result more feelings of control over a win or a loss.

Boosted Player Engagement: A fresh PvP mode would attract both new and veteran players. The new gameplay dynamics would provide a reason for players bored with Frontlines / CC to re-sub. New tournaments and events centered around the new PvP mode could promote the game. Outside the roulette system, entire FCs could participate in a tournament (especially if SE supported a monthly small tournament using an in-game sign up system).

Showcase of Skills: Players who enjoy leading can or forming smaller "strike teams" can utilize their skills in a way that isn't always possible in Frontlines.

Re-grouping & Morale: Re-grouping in Frontlines and making a comeback feels like luck less than strategy half the time because it depends on so many players behaving in a certain way, plus how the third team will behave while you're attempting a strategy on the second team. Those two combine, make it difficult to rally and get morale back up to continue the fight.

Too often do I see people just give up and start doing nothing when we're losing in Frontlines - Because they don't feel like they have any control over the situation. Control is important, if players feel like they can make a difference, then they're more likely to actively participate. If they feel like they cannot, then they're more likely to passively play and give up when things go wrong.

Increased Variety: Adding a new PvP mode diversifies the offerings within the game, giving players more options based on their preferred playstyle. This variety helps prevent burnout.

Even without a new mode, you could add a Rival Wings roulette, and that alone would freshen things up for a bit. Either way, Frontlines and CC by themselves are just not a diverse enough offering.