Yea, I went back and forth on whether mkII should get cloaking and mkIII should get missile-immunity or vice versa, but ultimately went with II=>missile-immunity. Basically you can spend that K to get a raid that's immune to its most common "can kill me quick" enemy (iirc) : missile and mlrs guard posts. You still have to deal with arachnid posts, though, and so on. If the enemy has enough ships, your raid's still dead.
Cloaking basically gives you conditional immunity to everything with proper tach drilling, so your raid starship can hit anything you can reach.
And the grav-immune for the big K investment + ASC gives you something that can pull off all the above in a grav-drill system, not worrying about grav guardians, etc. In some ways this is the least significant of the three new abilities, but since so little can counter gravity, it can be pretty powerful situationally.