Copying this from a GameFAQs post:
"Smash Bros uses lock-step, which you can't do on twitch shooters because there's input delay. If there's any packet loss at all, the game will stutter, or completely pause, until the connection resumes. The shooters you mention, use network prediction, so if a packet is dropped, it'll look like it is playing normally but in reality, your game is just predicting what the other players had done while it waits for the correct data to come through."
Nintendo right now uses P2P in their games, and as a result, if one person has a shitty connection, everyone suffers. On the surface, Splatoon's online looks miles better than Smash, but in reality, they're both mediocre overall, in fact, Splatoon 2's is worse.
The tick rate is so crap, there are times where I my shots make noises, but kills end up taking like half a second to register properly, and even a few instances where I just spontaneously die from damage that happened 1 or 2 seconds ago. I know 2 seconds doesn't sound like much, but in game, everything makes a difference.
I really hope Nintendo has dedicated servers ready for their paid online service, cause they are legit committing a crime if they think charging for sub-par P2P is acceptable.