Bigger install base than 3DS, bigger active base, better demographics.
I see no problem on World doing well in the west, so far impressions in Japan are positive, first in E3 there was skepticism but after TGS and all the previews from japanese media is doing fine, it won't do as well as the 3DS games, but that has to do with PS4's install base being unable to have games sell as much, Switch is at the same spot now.
The only concern with World I have is the GaaS aspect of it, as Capcom has shown to be terrible at handlig that, first the failure of Street Fighter V, and it didn't seem that they learn from Marvel, they really need to get that right.
Even if the game sells like Monster Hunter 4 I'd call it a success, for the increase of western sales more than anything, World isn't the end all of the series on the west, but more like the first big step, as to pave the way for the future of the series.
Capcom will push it more than Nintendo ever did, and Sony will too, they push Call of Duty when they don't need to, you bet Monster Hunter will get a big push, mainly in Asia where the series has stagnated as Nintendo has so little precense, think what Sony did with Persona.
I don't see the game as westernized, but more like modernized, it looks as what Monster Hunter would be as a big budget console title without compromising anything that makes the series what it is.