So having watched the Villarreal match, I feel that I now know why Origi doesn't get so much game time. It's because we have been winning most of our matches comfortably, and so don't really need him to change the game in our favour. He's only called on when we need him, a situation which is getting rarer these days as Liverpool become ever stronger (and additionally we don't play him so often to reduce the risk of him getting another horrific injury). But personally, I'd keep him around just for those moments alone, because even the best team in the world has its off days, and needs some sort of inspiration to get things going. And be honest: if we need to bring in someone to turn the match around, and you could sub in any player in the world, would anyone be a better option than Origi? Heck, would anyone even be as good of an option as him? I really can't think of anyone else.
As for comparison between him and Fairclough, I haven't been around long enough to see Fairclough play, but Origi isn't just a good substitute. Even when he starts, his impact is the greatest when the chips are down and we desperately need someone to pull multiple rabbits out of the hat. Like against Barca. That said, such situations don't come by often, and the only way it could feasibly happen in the PL is if the match against Man City is the last match of the season and we're trailing them in goal difference by -5 or something.
Last game of the season, we're top by 2 pts, but drawing at Anfield, City 8-0 up and thus winning the league on GD, comes on as a late substitute and smashes a 95th minute winner with the last kick of the game.
That'd do for me
Seeing that we're currently one point behind, for that to happen they'll have to lose one match before the last match of the season, and the goal difference will also have to be flipped in their favour.
I would too, but he owes us nothing and it's up to him.
As far as I know, he hasn't even been offered a contract extension yet. Unless that has happened, I can't agree with the "it's up to him" part.