Stellaris suffers from many things. Civ (and all other historically inspired games) draw a lot from the relatable content. If Ghandi threatens Cesar with nuclear weapons, it may be absurd, but we relate to this absurdity in ways that we don't relate to [randomized species A] threatens [randomized species B] with [deadly thing that is supposed to be more deadly than some other deadly things].

Stellaris is trying to be generic (the Stellaris world could be the background for almost any interstellar epic, it's full of little cameo references to every sci-fi classic the authors could think of), where Alpha Centauri went to great lengths filling the canvas, in one specific way.