The SP grinding for stuff did absolutely nothing alternatively beneficial for you. It was simply a boring grind against the boring robot AI. Not only is it extremely difficult to level up that way, it’s not even fun.
I'm all in favor of having tutorials, trials, and even having exlcusive content to be unlocked only through online playing is a great way to incentivise people to play online PvP and get better. I also think having a good lobby system and online ranking can help with that. And that's great.
I also think it's ok though for people to enjoy a game how they want to enjoy it. Some people just want to mess around in a story mode, and then maybe play some trials or practice mode to see if they can learn some cool combos, and have fun unlocking stuff against an ai, with no need to compete against a human.
To be honest, sometimes I'm that person. My favorite part of fighting games is learning how the game works, learning a character, theorizing about their moveset and possible strategies, going into practice mode and seeing if I can learn or get better at their combos. One of my least favorite things to do is actually play other people.