"primarily"
I am someone who legit bought the first 2 Splatoon games mainly for the campaign
I liked the TPS/Platforming mix and ink mechanics.
SF6 even has a full campaign mode, and VERY IMPORTANTLY local multiplayer.
It Takes Two for example is also a local coop game. you are not reliant on an active online playerbase. THAT IS THE KICKER RIGHT THERE.
if you sell a multiplayer only game, that relies on an active playerbase of dozens or even hundreds of always active players to work, then there will be a risk for the player to buy a game which will be unplaybe in a few weeks should it not catch on.
this risk is IMO a big hurdle these days as more and more multiplayer games fight for relevance.
even if Street Fighter 6 had no campaign and was purely VS, it still would ve a viable buy for many because you A: only need 1 single dude online to get a match going, and B: you can play it purely offline with friends.
I feel like battle royale is the one genre that just doesn't work as a pay to play game whatsoever. it is such a risky proposal for any customer to buy a game that needs 60 players to even function properly.
to function properly and do so without massive matchmaking times it's actually more like 1000 players, since regional matchmaking is a thing and you can't connect to an already ongoing match either.
so I think a game that's mainly 5v5 could work, but a BR in this day and age? I highly doubt that could have long-term success