Judging by what Arteta has said there it seems the long term plan was to play Partey in the inverted right back role. Speculating, but looks like when everyone is fit and he is selecting his best team, Arteta sees no room in midfield for Partey after signing Rice and Havertz, but he still wants the qualities Partey possesses on the pitch. Assuming the LB spot was Timber's, that frees up Zinchenko, Tomiyasu and White to rotate and fill in where need be when injuries and fatigue hit.
