Well, comparatively speaking inside the Pokemon series that is pretty huge. But it comes with the hardware upgrade, really - you expect bigger file sizes for digital titles, so this is nothing new. I'm surprised Let's Go Pikachu/Eevee were as small as they were, but whilst I am loathe to give SnS any kind of praise, I will grudgingly admit that they are more ambitious in scope than those games were. That doesn't necessarily mean there will be more actual content (although I hope there will be, because for crying out loud there ought to be) but...well, file size is no indication of quality or quantity.
But I can't help but wonder just how much of this is wasted or could be compressed, because Game Freak do not know how to make video games efficiently. I have a horrible suspicion that when these games get picked apart, the content will not justify the file size...because I doubt the way Game Freak make Pokemon games has really changed.