We’ve seen it what 343 is doing on Halo multiplayer. They try to make Halo a fast pace game, which is fine. We got brand new modes, Breakout and Warzone. And removed most game modes, so Arena lacks the playlists. It’s possible that 343 lacks the Arena on purpose. Why do they are getting all insults and risking their trustworthy? I think they did it on purpose to rip out stuffs that are not belong to them and insert their playlists. It’s not going to be hard for 343 to make classic modes. They maintained the least game modes, Slayers, CTF, and BTB to keep classic players. In the future, Breakout could replace all Arena modes and going Breakout style some how (problem is it has low population, so Breakout can be removed in future Halo). I am sure that 343 has new fresh ideas to add on that hardcore fans might dislike. 343 kept mentioned Warzone mostly everywhere. They could add some new Warzone variations in future. All their excitements on E3 and Gamescom came from only Warzone? Nah, they have its variations still on progress. If their all excitements were came from just Warzone, they are just stupid and lazy company. Also, REQs were created for Warzone to balance the game and REQs pretty much ruin the Halo 5. So, only way to cover the REQ is Warzone. However, I do think that current and previous DLCs are trash, should’ve contained at release. I want to believe that 343 is going to add some fresh modes than REQs. I hope.
They chose their Arena modes to focus on competitive and eSports play.
Slayer, CTF and Strongholds fill the basic niches for eSports gametypes; standard death match, objective delivery, and area control. Breakout is another common form of game type thanks to CS:GO and others.
Doubles is more of a niche game type, FFA is one of those expected playlists for this kind of shooter.