AI vs Human Opponents
Keep in mind that the Blood Pass xp you gain is calculated (somehow) by adding up almost every action you take across an entire game.
So a multiplayer game where someone forfeits early won’t give as much as a full 16-turn game against the AI, because there were less actions taken.
But a full match against an incompetent AI, where you barely had to dodge and/or there were sometimes no standing opposing players left to hit, will also give less xp than a more balanced game that stayed active and frantic for all 16 turns.
Which game mode works better for you might depend a little on your team, playstyle, and the calibre of opponents you’re finding. But the differences aren’t that extreme, so the intention is for players to go with whichever option they enjoy the most, not mindlessly grind in a game mode they hate in the name of efficiency.
Note: AI pay nicely and it’s quite fast to grind a few 4-0, 5-0, 6-0 against it.