I'm pretty sure, carrying more than 2 weapons helped in HL's case.
Carrying two weapons can make sense:
1) If the weapons are decently balanced
2) If the weapons are everywhere
3) If the character is going to be limited and not some god
4) If the game features load-outs you pick prior to a mission
5) If realism plays in at all
6) If the game is on a console, where no one has yet figured out a good way to use multiple weapons
Duke hits one of these, #6. It fails at every single other one. I'm perfectly ok with only two weapons in Halo, as I know that I can find any other weapon I want laying around at any given time since weapons are literally everywhere on the ground - I never felt like I was making a tradeoff and typically felt like I was making a strategic decision. I'm perfectly ok with only two weapons in Gears of War because your weapons fall into two categories: machine gun and special; you pick the machine gun you like best and the special you like best and you go. I'm ok with it in Call of Duty because I'm using a setup I created specific for the level and, again, it feels strategic to me. These all reminded me a bit of Rainbow Six.
I was not ok with it in Far Cry, in which I despised having to choose between sniper and rockets and ended up never using the damn special category because I never trusted that I'd have ammo when I needed it.
And I'd resent it in Duke because so many of the weapons just aren't useful enough to ever pick up. Why would I drop a machine gun or shotgun for the freeze ray, other than a contrived part of a level made just for it?