Arteta may well have said he wanted him / supported the signing, and may even have convinced the player to join, but that doesn't mean he was 1st choice in that position/role, and may well have been a case of if we spend 45m on Partey we don't have anything for anyone else. In saying that I realise Willian was one of the first signings last summer, but if we're keeping our powder try on bigger fish it makes sense to get what we can when we can.
IIRC there was a comment made in the media claiming it was not a case of either/or for Partey/Aouar as had been reported at the time, in which case I call BS as we've seen no signs of any additional funds being made available in Jan. We've been supplementing via loan players (MO, Ryan, Ceballos, Mari, Soares) and Bosmans (Luiz, Willian) for the last 2 seasons and it doesn't look like changing anytime soon.