I don't want to speculate about all the other stuff, but I'm pretty well convinced that Partey is not the player Arteta would choose to play in what I (and I think he) see as the most important role in this team.
He lacks a feel for the game that his crucial to being elite in that Number 6 position in a team which plays in the way we do.
By that, I mean acting as a pressure gauge for the team by sensing where the momentum and energy in the game is at in any given moment, and controlling the tempo and rhythm the rest of the team play at. Slowing it down or speeding up in the right moments, knowing when to stay compact and stay put, and sensing when the moment has come to loosen up and inject more energy and pace into proceedings. Not just for your own game and what you do with your passing or positioning, but the ability to command the rest of the team to adjust what they're doing to fit what the game needs in each moment.
For me, as good as Partey is, he doesn't have tjose qualities. And it's more a failure in game understanding, personality, and leadership as it is anything technical or physical.
And it's why I'm so excited about the prospect of Rice joining the club. I think he can be every bit the player I described above.