Do we have comparisons with Worlds physical release and sell through? And digital for that matter. I'm surprised considering how much bigger Switch's install base was but I guess its software market (in terms of big sellers) is more crowded than PS4's.
People generally tend to overestimate the effect of install base. Especially for system sellers it doesn't matter that much, per the definition of system seller the ones wanting the game will get the system. And as both PS4 and Switch improved (and 3DS for that matter) in Monster Hunter week, it is clear that the game is a system seller. Also I think in Japan pretty much every possible fan on MonHun already more or less knows about the game series. So similar sales for World and Rise (which obviously is happening) isn't that surprising. We could have speculated if Rise as a game draws in more people, but it seems it is the same base.