ALIENS: FIRETEAM is an absolutely horrible source and reference when it comes to realism. The Drones and Warriors may be 3x or 4x more durable than the Aliens in the movies, but then on the other hand you have to remember that the marines in A:FT are at least 10x more durable, strong, accurate and aware than than the marines were in ALIENS.
In ALIENS pistol bullets ricocheted
off of the Aliens when shot at more than seven or ten ft away. Vasquez killed an Alien with her pistol when she emptied a whole clip in it from POINT-BLANK range pointed at a soft spot area on the Alien.
It's safe to say that shotguns are probably as useless as pistols against Aliens from afar, but up-close they're obviously lethal against them, especially when shot inside the mouth of the Alien.
Again, Aliens ARE strong and durable as hell. They can mess up or even punch their way through metal doors/bulkheads, they can withstand beyond extreme temperatures, environments and heat (molten lead, plasma jet blasts etc.) - and so on and so forth.
The reason pulse rifles and smartguns are so effective is because they're advanced high-velocity weapons that fire explosive munitions - i.e. the rounds not only penetrate from afar but also explode, which has a boosted effect against an acid-for-blood hyper-pressurized sealed exoskeletal creature like the Alien.
I personally would like to see the Aliens to be slightly more durable than in the movies. But even more so I would like to see the concept of limb regeneration and general regeneration abilities cemented as a default trait as that was a part of the original Alien creature's quirks and chatacteristics, which R. Scott has been hinting at in interviews regarding the creature we got. For example, I subscribe to the notion that the Sentry Guns DIDN'T kill or permanently incapacitate that many Aliens in ALIENS, as most of the Aliens regenerated themselves back to their full combat capabilities within hours. In order to kill an Alien you need to blast it to pieces or destroy its head, or 'simply' remove the head from its body.