For those too young to remember, back when Halo was huge every gaming publication was always like “is this new shooter X going to be the Halo killer?” Every time a big multiplayer shooter was announced, there was speculation about whether it was going to be the Halo killer.
Now that Halo is dead, which game was the Halo killer?
I think battle royale in general was the halo killer.
Both because Fortnite and Apex Legends have I think occupied the attention of Halo’s traditional playerbase and age range, and because the Halo dev team spent some time chasing the battle royale format and wasted time and energy on that during infinite’s development, IIRC.