or adding dual wielding, which fundamentally changed the combat loop of Halo, or destructible vehicles/hijacking which fundamentally changed the vehicular gameplay of Halo, or the lack of health packs, or anything that isn't Halo CE essentially
how can you honestly call any of the Halo sequels Halo. Give me a fuckin' break.
Play a match of Halo CE slayer, play a match of Halo 2 slayer, play a match of Halo 3 slayer, play a match of Halo 2 Anniversary slayer. Then play a match of Reach slayer, a match of Halo 4 slayer, and a match of Halo 5 slayer. Pretty certain the 4 former games will play closer to each other than the latter 3.
I think aside from small changes in movement speed, fall damage, health/shields post CE, and different weapons, vehicles, maps, the biggest changes are things like dual wielding, vehicle boarding/destruction, and equipment for games CE/2/3.
I get what you're saying though.
Edit: the other shoe hasn't dropped yet. We've only been shown arena game play. We still haven't been shown their massive changes to BTB or whether they're brining non-Arena/Infinity back. These 3 weeks aren't necessarily going to be indicative of the final game at all.