I don't want to do my Nintendo fanboy, but I just remind that Odysee had performed 60% of this sale in the same amount of time (2M in 3days), with an installed base of Switch 7 times inferior than the PS4 today.
And Killzone: Shadow Fall sold 1 million copies on an install-base 27 times smaller. Past a certain point, the degree to which install base affects the sales of individual games diminishes rapidly. As quick noted, Galaxy 2 actually sold less than its predecessor despite the Wii's install-base being several times larger at its launch. Does that make Galaxy 2 a massive relative flop? Of course not, because by that point other variables were far more relevant. Those same variables are what allowed SMO to sell more than G2 on less.