The same downplay was also there for Pokemon Let's Go... until the 10 million number came out. So, we shall see.
Would 10 million be considered a success for a mainline Pokémon game?
Historically, crossing that in a month or so would be best described as "fine." As a total lifetime that would be low. However, it's hard to judge where the game is going in terms of its total until either Nintendo gives us a PR statement or we get to the next quarterly report. The opening week is much, much larger than Let's Go from what we can see but we are still a week away from the big Holiday shopping period kickoff which will factor into the sales trajectory of Pokemon significantly.