The issue was that the plasma caster mechanics were all wrong.
In the first game, the caster was powerful, but it needed to charge between shots to 1-hit an Alien and the targeting was fallible. It was one weapon amongst many, not the default, primary choice of armament. Could it be powerful in the right hands? Surely. But it had to be properly used. Spamming it just left you without energy, surrounded by Aliens.