The thing is that the Alien movies feature combat with more than one Alien exactly twice, both times being in Aliens. In both those cases, it wasn't one marine gunning down a bunch of Aliens, it was a team of marines holding out. It suggested that Aliens respond to force in kind, not that they used swarm tactics as a general thing.
The combat system doesn't limit long-range battles in any way, perhaps apart from enemy health and that's not exactly part of the system. Even Predators go down very quickly in MP, allowing you to switch targets. I even watched my younger brother take on three Aliens at once as a marine and win. It's definitely possible.
Personally, I believe the constant desire of media creators in this franchise to increase the scale only ever harms it. The AvP comics and films are good enough evidence of this. A focus on smaller-scale confrontations between more evenly-matched enemies that results in confrontations sometimes taking a while to resolve is entirely in character for each individual franchise and something that should be supported.
As for the weapon set, I think it reflects the reduction of scale. Some weapons never really needed to exist, such as the grenade launcher or rocket launcher (both of which are made redundant by the pulse rifle in any case). The minigun was a fun addition, but combining it with the smartgun was pretty much the right move, since there's small point in having two powerful, rapid-firing heavy weapons in the game.
It seems that we value different things, though. I prefer the horror element to be a part of the base gameplay and for the decisions in the game design to reflect that.
