Who are you to say what does and doesn't belong?
Supermutants were the antagonist of the first game, they've been part of the game since the very beginning. Ghouls aren't as important to the series as supermutants are.
What we see is just remnants of the Unity, a group that in the bad ending for F1 made all of humanity into supermutants who, unknown at the time, are sterile which caused them to die off after many centuries.