I think 18 million is a little to much in only 7 weeks. Also, why do you think it will sell so much more in Nord Amerika than it will in Europe and Japan?
Metascore means nothing to the millions of fans in the series. At least from what i can tell everyone worse generation seems to be XY. While hardly any complaints come from sun/moon. At least to my understanding. Even i see the quality difference between the 2.
Anywayz because of right now we have NoA at 3.7mil (though its 10 days vs Europes 5 days) while europe is 1.5mil. Japan is tracking below xy but i think itll pull evenly with shipments. NoA at 3.7mil sold should have about 5mil shipment if not more and i think theyll ship another 4mil with how much the game is proving to be a major hit.