Considering world is at over 16.8 million as of the December 2020 this seems like an awful prediction. Especially with the switch being so much more popular than the ps4 in Japan. I'm not expecting this to sell as much as world but 7.5 seems way to low, 10 is the floor for this one.
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!