MHW will not bomb in the West. That's not even up to debate. But it's not enough for this game to not bomb. It must be able to attract a sizeable audience on top of the audience that was traditionally buying MH on 3DS (around 1m gamers). The main reason of MHW existing is to expand the franchise popularity in Western markets. If it sells, say 1.5-1.6m outside Japan, do you think investors will be happy? All of this by forgoing a couple of million fans in the domestic market, with a much bigger investment? MHW looks really good... for a traditional entry in the franchise. This will please fans in North America and Europe, and might attract a few people that never tried the franchise. The issues is, will MHW be able to attract a lot more people? That's a harder question. Graphically it's not a showcase, and the gameplay might still be a bit stiff for the general public.
Of course it wasn't about the platform choice. Point is, investors don't typically care. They see a huge ROI from Ultra Street Fighter II on Switch, they see Switch selling like hotcakes, and then they see Marvel vs. Capcom missing its target by a huge margin. They will ask "Where are Switch games?".