After reading the thread speculating infection in Ghosts of Meridian I decided to check out the lore a bit. Found this,
This world was discovered by the Covenant Navy in 2548 and attacked, the Covenant attempting to cut-off the colony’s supply lines, but the UNSC Defense Force was successful in driving the Covenant off the colony due to an extensive orbital defense grid and a large air force, continuing to fight off Covenant attacks for the next three years until it was finally glassed in 2551.[5][1]
It would make sense for them to add in warzone firefight as a simulation (that’s what warzone is) of the past battles that happened there. Plus why would they tease firefight and no other game modes if they were just going to release the mode 3 months later? And the meridian attacks are a great way to make firefight against covenant more relevant to the current game timeline. Covenant are just not as big of a threat as they used to be in the current halo universe. They want to build hype for each upcoming update. Anyway, makes sense to me.