It's interesting to note that I remember the Wii U's online numbers were similar when BLOP2 launched (and that was coming out a couple weeks after the other versions). The media blew up the fact that it was so far behind the 360 versions numbers (fair comparison) and everyone declared the Wii U's online DOA. Now we see the same community going strong even after a sequel has been released and regardless of how poorly the Wii U's versions have sold in comparison, a healthy online community are what anyone plays these games for and if it can remain consistent for over a year and a half after launch, that's a good sign for the Wii U.
I don't know Killzone's online numbers near launch but just like people pointed out those COD games are the only Wii U FPSs (as if people don't have any other choice instead of maybe they do have other choices but choose to play the game on that platform and with that community) that also means that the online FPS community won't be as fractured amongst the over saturation of the genre on other platforms. It seems to me that besides a select few titles, most FPS such as KZ, enjoy a surge in online popularity at launch which then dies off after a few months as the hype dies off and/or other games come along. For a games that is supposed to be played online, that is the worst if you pick it up after that surge and find multiplayer to be a ghost town.
I think Nintendo's hidden strength in the way they've built their online communities is like the way their sales for their "evergreen" titles work, they are a "slow burn" rather than the normal hype cycles with AAA games on other platforms. From how consistent or surprisingly strong I've heard online numbers were for some Wii games, I don't think online is quite the weakness for Nintendo as people suggest since longevity can be more important than sheer numbers for the gamers.
