Well when we can argue yet another factor for example attach ratio, it would seem that MHW has the biggest disadvantage. MHW has about a 40% attach ratio, compared to most MH's only doing about 10-20% attach ratio. Saturation point is at its highest for PS4 MH fans. But I have already argued for those things multiple times before. My point is the legs are quite standard, and one shouldn't expect too much more from MHW.
Well two things before you bring in attach ratio, 1: it still depends on what titles were released with it at that time (on the 3DS in the same timeframe for example) and 2: look at the titles released in Japan, which sold the most and continue to sell the most. The 3DS for example had together with Monster Hunter, many games like Pokemon, Smash, Yokai watch on it released which sold big numbers over a pretty long stretch. Those factors can be taken into account. This MHW had, in my opinion, a clear and open way to have great legs in Japan.