My opinion (and I assume TC’s reasoning behind the decision to exclude HOD from the multiplayer) is that weapons shouldn’t be included in versus only for the sake of variation.
I don’t think there’s an actual need to have it in the weapon pool. Dropshot already fills that role of a weapon that can ignore cover and force players to move out of cover (HOD was mostly used either by firing from higher ground or aiming past cover from the side to hit enemies behind cover). Dropshot, unlike Digger in Gears 3, has a wide instakill radius too. So it’s kind of like Digger and HOD combined.
Dropshot is also far better balanced than HOD. HOD was always either overpowered or underpowered in versus. In the long run, putting weapon balance before anything else when deciding what weapons are available in versus and how they function is going to be healthier for the game. And Dropshot serves the same purpose as HOD, but better.
If TC can find a way to redesign HOD so that it’ll have a unique role in versus while also making sure it’s in balance with the rest of the weapons, then I’d be all for returning it to versus in Gears 6.
EDIT: Also, adding weapons into the game after its release is not as simple as one may think. The maps need to be designed to play with the new weapon AND it would have to be made sure the newly added weapon would be in balance with the rest of the weapons. It would require testing and tweaking of (potentially ) several weapons, which could take anything from weeks to months. And also most likely more tweaks to weapon balance after the weapon’s introduction.