It's true that historically there would be always at least 2 men designated to one lmg or handheld AT weapon, just becouse how much ammunition it uses. That's also why squads did never use more than 2 of such weapons. One per each squad was already quite a lot.
On the other hand in the game average squad size is 5, instead of historical 10. That means its ok to designate only one guy for the heavy weapon, but just like in case of real squad they should never have more than 2 weapons per 10 men, so the real solution and good thing to do is just limit all squads to have no more than one special weapon.
Yeah, I can't see this happening either. If Relic wanted to make two men load and fire a heavy weapon, they'd have implemented it on release - and let's be honest about the obvious alternative, one guy standing around unarmed in a squad is friggin' stupid. People were outraged enough when they had the Scripts do it a bit in the campaign, making
everyone do it in multiplayer would be seen as nothing short of ridiculous.