I don't see how Nihilus is useless on GW. If anything using him (at 7* for me) has made GW even easier, thanks to his primary attack which gets rid of annoying buffs, helps speed up the annhiliate attack for any potentially long battles, and he also proves rather valuable when I use him as a lead in the late nodes for my sith toons who can benefit from the health drain at the end to close out a show.
I also agree, by letting him bank the annhiliate attack to wipe out a select heavy toon is overkill IMO (even though, sure I'd love to have that option given all the $ I put into him)