Looks like Smash Ultimate has a good chance to sell more than KH3 in 2019.
KH3 - 755k (already below Smash Ultimate)
Smash - 505k (strong number every week and a few more updates to drive the sales)
KH3 is already charting below Smash
Smash Ultimate - 3,6 million physical - 2018 and now at Feb1 2019 Smash Ultimate is above 5 million sold-through
Should be around ~500k alone in January Physical+Digital