Let's take a deep breath for a moment and remember Switch sold 360k when MK8D launched.
Mario Kart came out in April and July is slower than April in terms of sales.
Mario Kart was the Switchs second big game after Zelda.
Mario Kart is bigger then Splatoon. Splatoon is big but its not as big WW as people make it out to be. Its a huge deal in Japan but everywhere else its not a huge deal while Mario Kart is a huge game worldwide.