Might be true today. Everyone here has to remember NW, which is arguably the larger MP scene in M&B has always built upon events. The peaks, just like shown in the MNB Central statistics, has always been during weekends when NA and EU hosts their massive regimental line-battles filling several 200-slot servers to the brink. So in a way, calling the MP scene dead is unfair. TW Forums have 8.000.000 forum posts. The FSE (NW DLC MP) forums have about 2.000.000 forum posts. It's evident both communities has been very alive historically.Another thing when comparing warband MP to SP stats these days is that Warband MP is quite dead... It is an old game with only the dedicated MP players who have thousands of hours in the game playing it still. Most of the remaining casual players are on SP now, since there is no massive MP scene.
Unfortunately, there are no Steam achievements for playing NW. The Steam achievements does only register Native multi-player kills, wins. etc.what @Lord Brutus pointed out about NW is something we're not sure of and we shouldn't presume the same achievements apply for that mod.
NW/Native servers has self-hosted leader-boards since a couple years back though. A few NW LBs: Groupfighting, Minisiege, BoB_Groupfighting, and NRP is releasing in-game player statistics next month.