Hard to say. Monster Hunter is a very popular franchise, no doubt, especially in Japan where it is consistently one of the top three most popular third-party series (along with Final Fantasy and Dragon Quest) and a reliable system-seller. World is by far the best-selling game in the series at 16.8M copies, but it was a multiplatform game and we have no clue what the platform split is. All we know beyond the global total is that it did well enough to make it into the Top 10 of 2018 in the U.S. (overall and for both the PS4 & XBO individually) and was the best-selling PS4 game ever in Japan. It was also the first and only entry in the series where the clear majority of sales came from outside of Japan, which is why it sold as well as it did. While previous MH games never sold over 2M copies outside of Japan, World put up outstanding numbers outside Japan. Even though it was the best-selling PS4 game ever in Japan, that's not saying much as it apparently didn't even quite hit 3M even when including digital (nowhere close to #1 in the series in Japan), which would leave at least 13M for elsewhere.
The PS4 Japanese numbers were 3.17million, there's a platform breakdown in my earlier post and also a link to more detailed numbers.