I’m not sure the specializations in H4 added much to the game. Instead, I think they detracted from it. Part of the problem is that every specialization needed a perk, and some of those perks required eliminating what used to be a standard gameplay element (like resupply). It also led to a proliferation of perks, most of which are little-used. And little-used perks do not add anything to gameplay.
An arena shooter requires even starts. That doesn’t mean (in my opinion) the exact same weapons or abilities, but it does mean that the starting options must he reasonably equivalent. Every option that is added is another option that needs to be balanced. So for weapons we have 4 precision, 3 automatic, 3 sidearms that need to be balanced. For AAs, 8 armor abilities that need to be balanced. And 18 (9 + 9) perks that need to be balanced - of which specializations contributed almost half (8).
I don’t mind the concept of specializations, but I think the game would be better if the specializations were recognition of specific types of gameplay (uber-medals) rather than a way to get perks. So if you want Wetwork, assassinate a bunch of people. Operator? Rack up those wheelmans. Gunner? Blaze away with the chaingun. The specialization should be a top commendation earned for completing a set of specific commendations. It should be its own reward.
If done that way, the specializations would actually be much more meaningful. Most of all, they would not require any perks, and some of that functionality that was removed simply to have a perk could be returned to all players. Lastly, it helps avoid Halo slipping into a class-based shooter, as fundamentally, specializations done the way H4 did them are really classes. Done the way I suggest, they are bad–Yoink- commendations.