Again I agree with you and this is the only position that really worries me as it's so obvious that even a below average Partey is so superior to any of the options we have ATM.
The guy's contribution to the team is just unbelievable...it seems like he single handely runs our midfield and dictates tempo no matter how poor he is. I still believe his absence was the main reason we lost to Man U. I don't know how to put it but he just makes us look like we are playing an extra man in the centre.
If we are spending money, that is the position I believe we should spend anything to get adequate cover for. Partey is irreplaceable in this team and like you said without him the dropoff in quality of our play is just to obvious.