Modern warfare 2019 did this very well. For the majority of players who want some casual fun, create a normal/casual playlist. Allow 3rd person mode in it as casual players may want to switch to it to see all of the expensive armors they purchased on the store. For players who enjoy the hardcore arena Halo experience, create a hardcore/ranked playlist. Restrict it to 1st person only so there can be no corner peeking and whatnot then promote it with different events much like every single major FPS with ranked. Create some awesome tournaments on the official Halo YouTube channels with chances for players to get themselves known
Would not only bring in a HUGE wave of 3rd person shooter fans (Fortnite) but would massively boost the game’s popularity by giving fans tournaments to show off their skills and go back to the core Halo experience they know and love