World released on three platforms so far (who knows, they may have an upgraded version in the works for PS5/Series X/PC). If you averaged let's say 17.5 million MH world sales (it's been some months since 12/20) that's 5.83 million MH world sold per system on average. So if MH Rise sold 7.5 million on Switch then it would have sold considerably more per console released on (1) than MH World did (the PC sales being TBD for now since Rise hasn't released there yet). So 7.5 million on Switch alone is kind of crazy!
You can make the same argument either way by using the same point you just made. Aligning launches, World did 5m on launch with 2 platforms (PC came later) and Rise did 4m on launch with 1 platform. That could be used to argue that Rise will do better than World. 10m is not out of reach.
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