Install base is a function with respect to the # of system sellers and is not strongly correlated to the first week sales performance of separate games ...
3DS's larger install base was mostly down to getting Animal Crossing and Monster Hunter before a mainline Pokemon entry appeared ...
The more people own a system the more potential buyers, that’s general logic. To call S/S a mediocre opening while ignoring install base is ignorant imo.
And how do you explain X/Y selling more than Sun/Moon despite having half the install base?
Half the install base? The 3DS had around 14m in Japan when X/Y released, compared to 10m of S/S.
He's asking how you can explain X/Y selling more than Sun/Moon even though X/Y released on a much smaller install base than Sun/Moon did? By your first point, Sun/Moon should have sold much more because when those games came out, it was on a significantly bigger install base and selling to more potential buyers. Especially when you consider when those games launched, hot off the heels of Pokemon GO and its worldwide takeover bringing Pokemon close to the levels of popularity and awareness it was back in its peak in the late 90s.
You can't just multiply the Switch's install base and apply the same to Sword/Shield thinking it will sell that much more. It doesn't work that way and it never has. Every Nintendo handheld that has had 2 mainline Pokemon games, the 1st one always outsold the 2nd one.
Game Boy/Color: Red/Blue > Gold/Silver
Nintendo DS: Diamond/Pearl > Black/White
Nintendo 3DS: X/Y > Sun/Moon
Bigger install base be damned. Because a portion of the audience are usually satisfied with just the 1st set of games. Add to that, the remakes of a prior generation or enhanced versions Game Freak releases in between generations, by the time the 2nd generation comes out, those people who skip out on it do so because they've already had their fill with Pokemon on that system and are ready for the next. And this also goes for many of Nintendo's other franchises, not just Pokemon.
Mario Galaxy 1 > Mario Galaxy 2
Ocarina of Time > Majora's Mask
Twilight Princess > Skyward Sword
DKC 1 > DKC 2 > DKC 3
Wii Sports > Wii Sports Resort
Metroid Prime > Metroid Prime 2
I could go on and on.
Most of the time, a bigger install base did not equate to better sales for the next game.