I think the perceived issue is more clear if you compare Rakhas to their most obvious "competitors" in the world of spoiler NPRs:
I mean the Precursors. Precursors typically involve fighting some combination of naval, STO, and ground combat forces to secure the planet(s) they defend. In return, you obtain not only a nice planet with decent colonization potential and perhaps some minerals, but also often a hefty stockpile of prepackaged gallicite missiles and most importantly some alien ruins to exploit for fun and profit. The size of ruins does tend to scale with the size of defending force from what I know, as well.
By contrast for fighting Rakhas you get nothing special besides a planet and there are many of those in the galaxy to be frank. That being said I would not presume that we should get something more, I think of Rakhas as being more for flavor than any mechanical benefit, really they serve to make the galaxy a more dangerous place and to provide some flavorful ground force actions besides messy homeworld invasions. In that sense they are more similar to the other spoiler races in that you don't get much from actually fighting them, and what I've described in the previous paragraph is really an exception rather than a rule albeit hardly exceptional since they are so common comparatively. The thing about Rakhas is that they can, if the player wishes, be generally ignored which I will say is a unique mechanic at least.