I suppose you missed the part of my post where I asked about situations where both players own the game.
I never once suggested it was about p2 getting free games.
Nah, I saw it, but the thing is that technology is based on player two playing in player one's game on player one's console. Regardless of whether both players own the game, player two is not actually playing on
their account on
their game.. They're effectively just an offline guest account on player one's console. That's how it works.
So the system simply can't allow for player two to unlock trophies at all, by design, and it never will. Of course, there's nothing to stop you playing Towerfall for an hour and then the other person streaming it for the next hour and you'll both get trophies that way, since you both own the game. It'll just take twice as long.