While you are correct about it not outselling World, your reasoning is fairly off. It came out last August when there was only a few million Switches out there. Switch was selling out routinely so there was no chance Monster Hunter could boost sales. Lastly, it came out on 3DS as well in Japan. This fact alone ensured the sales would be limited as there are over 20 million 3DS users in Japan who would have 0 incentive to try fighting for a Switch to play Monster Hunter at that point.
The game has reviewed well and was received well in Japan. That tells me that you were just trolling with those comments. With all that said, I completely understand how the quality of life improvements and graphical upgrades will make going back to Monster Hunter on handheld seem like a terrible idea. I am one of the few people with the ability to go back to Generations Ultimate because I see it as the handheld version vs the full console version being on PC (or PS4/XBOX One). However, people that are looking for the comparable console experience from Generations Ultimate are likely going to be disappointed.
Excuse me but I do not troll. And I never said the game was bad, I simply explained why most Japanese gamers weren't interested. And no, XX was a massive drop sales wise and reception wise by the general audience in Japan vs X because XX was a moderate upgrade of a game that was already just a greatest hits version of old stuff. X was supposed to be a stop gap, it getting an ultimate version clearly didn't go over well. And I already acknowledged the 3DS version, hence why I said it was a port being one of the reasons it failed to sell like Monster Hunter should. And the install base at time of launch argument is BS. Zelda, Mario Kart, Splatoon 2 have all outsold it by enormous margins despite launching during that same period when "few" Switch's were out. Monster Hunter XX Switch didn't sell as well because most MonHun fans were sick of the game by that point and the port did nothing but wrap itself in HD textures and a few ver modest post processing effects.