make it so that if you don’t select at least three modes that are different at their base (Ex: You can’t select just Slayer, SWAT and Snipers since they’re all Slayer variants, nor could you just select 4v4, 12v12 and FFA Slayer etc.) you don’t qualify for any Daily + Play bonuses.
If you just want to play Slayer, you can, but you only get your 100EXP or so per match, plus whatever Challenges you can do in Slayer.
But if you want those bigger, juicier 500/300/200EXP play bonuses per day/match or whatever, then you have to sign up to play other modes as well.
Because as Sketch has said, both about Infinite and previously in MCC (and H5 I believe too) Slayer, as a standalone gametype, has a massive negative impact on every other gametype in the series, often getting to the point where you can’t get matches in those modes. I believe someone on the old Waypoint forums pointed out that despite how much people complain and whine, if they went by the pure numbers, all the other modes are basically wasted Dev time - you could ship Halo with just Slayer and have Infection/Grifball rotating playlists every so often and like 90% of the Halo population wouldn’t notice or care enough to say anything about it.
This method gets the community what they want (the ability to pick what they want to play) and 343 what they want (the ability for most gametypes to have a healthy enough playerbase that matchmaking works and gets good matches).