Nintendo is definitely making a big deal out of this game. There is both a Splatfest and a tournament in Seattle before the launch of the game. (Not sure if they announced some other tournament for people who don't live in the US.) I don't recall what Nintendo did before the launch of Splatoon 2, but I do know the install base for Switch is a whole lot bigger this year than in 2017.
I do think Splatoon 3 is going to sell even better than Splatoon 2, and I wouldn't be surprised if it makes it into Switch's top 10 (which is getting harder and harder to enter.) Out of Switch's 10m+ sellers this is the youngest franchise, and I think it still has room to grow.
curl-6 bet me that PS5 + X|S sales would reach 56m before year end 2023 and he was right.
My Bet With curl-6
My Threads:
Master Thread, Game of the Year/Decade
Switch Will Be #1 All Time
Zelda Will Outsell Mario (Achieved)
How Much Will MH Rise sell?
My Bet With Metallox