Here’s a list of all weapons and vehicles in past Halo games that did not have an appearance in Halo 5. It would be cool to get some of these in updates.
Starred items are weapons that don’t have any similarly functioning replacements.
Halo: Combat Evolved - Flamethrower*, Plasma Rifle
Halo 2 - Brute Plasma Rifle, Brute Shot*, Sentinel Beam*, Sentinel Beam Major*, Non-detachable Machine Gun Turret*, Spectre*
Halo 3 - Heavy Flamethrower*, Missile Pod**, Brute Spiker, Brute Mauler, Gravity Hammer*, Spike Grenade, Brute Firebomb*, Hornet, Transport Hornet*, Elephant*, Anti-Air Wraith*, Brute Chopper*, Brute Prowler*
Halo Reach - Grenade Launcher*, Plasma Launcher*, Plasma Repeater, Needle Rifle, Focus Rifle*, Concussion Rifle*, Falcon*, Revenant*
Halo 4 - Sticky Detonator*, Pulse Grenade
**- Rocket Pod is very similar and mostly replaces this, but only the Warzone-exclusive ONI variant can lock on to Ground Vehicles.