No idea what you're basing that on. He's still surprising me almost weekly with how good he still is. Finishing, passing, energy, vision, command, all still there. Covered every blade of grass in the cup tie last night. Maybe he can't do that every week anymore but if he does that 75% of the time he's still a huge player for Liverpool. He was the difference last night.
I can understand why he'd leave if he's getting a 4 year deal over in LA as opposed to a 1 year deal at Liverpool. And there's absolutely no chance of him signing for Man City (or anyone else in England)