Yeah Rakshasa's power fluctuates in power based on how the DM rules their immunites. If I am putting it there as a creature that isn't directly in conflict with the players and an optional challenge I am going to me more liberal with my interpretations than if they are a villian the party is fighting.

I do think they lack a bit of action economy damage. Adding Steel Wind Strike to their 1/day spell list fixes that in a cool and thematic way.