I'm watching Fabian Ruiz play for Napoli against Genoa and he's just a joy to watch, his passing is sublime sometimes.
He plays on the right of the midfield in a fairly fluid 4-3-3, and he consistently gets on his left foot and finds attackers in the penalty area with his passes. He still makes mistakes, but there's immense potential there.
We probably couldn't afford to buy him outright from Napoli, he'd be more expensive than Partey i'm guessing. You could maybe try a deal involving Lacazette or Guendouzi, but it's a long shot.
I really think he'd be more suitable than Partey. Like Partey is good defensively, he's a solid passer, he can dribble and he's got a decent shot, but he's not a creative player really. He makes us better and more solid, but does he elevate us to a Champions League level?
Fabian Ruiz and Dani Ceballos either side of Xhaka or Torreira in a 4-3-3 is potentially a seriously good and creative midfield.
He has dominant performances against Barcelona, Real Madrid and Liverpool. He is a world class player in my opinion, so he definitely elevates the standard of the midfield. He gives us tactical flexibility as well, was he can play in a two or as a lone pivot in a 433 (in my opinion).
Ruiz is a really good player as well, but I think Partey is better defensively, and will let us transition to a 433 in the coming years. I also think the midfield you mentioned lacks a bit of dynamism.
I hope the club is aiming for something like:
----------Partey---------
---Aouar-------Saka-----
as the midfield 3 in the future.