Delayed ports always do much less than the first launch time, even when it's games coming out on other platforms like 3/6/9 months later. Imagine a game coming out 4 years later?
I think people really have a warped idea of how much initial sales can be sold for most games once the FOMO has been gone for subsequent SKU releases.
It's FF discourse again... I tire of it in general.
Being multiplat is a relevant part of the equation in terms of Square gaining potential sales but it's not really the supreme magic bullet for them. There's plenty of things they can do better in terms of release schedule/marketing(they're complete dogshit at it) and a bunch of other things related to project choice(s) and management.
Hopefully they can figure it out, as a fan of FF/DQ since the 90s and it kinda sucks to see well reviewed games not do the numbers and profits SE would like.