Of course Smash will sell more. I'm sure Pokemon Let's Go will sell well but its a side game, with the real Pokemon game coming out next year. I think it's possible Let's Go sells 10 million lifetime just because it's Pokemon, but Smash is a guaranteed 20+ million considering Mario and Mario Kart are heading that way as well and I suspect Smash will sell more lifetime than those two. The core Pokemon game coming out next year I think has a good chance to beat out Smash as likely the best selling game for the Switch lifetime, but Let's Go no not even close. I think Let's Go versus Splatoon 2 is more interesting.