Ok mate.
I'd be interested to start with to find out why you think his passing is so poor. Is it passing stats? If so, these can be so so misleading and don't tell the full story. So many CBs passing accuracy stats are boosted by short passing between themselves, the FBs and the DMs. With no high pressing from the opposition, you can keep ball easily for 5 mins doing this, never get past the half way line, and maybe get 7 or 8 touches during that time.
Mason doesn't do that. If he has time on the ball he get's his head up and is always looking for a telling ball pinged into the forwards or the advanced midfielders. Some of these don't come off because they are difficult passes to execute, especially when playing under Koeman and Allardyce when options and player movement is minimal. But under Silva, you get the impression that there are going to be a lot more options for him, so you would hope that his accuracy stats would improve. In Saturday's game for instance, there were at least 2 of his pinged balls that led to goal scoring opportunities. None of our other CBs (before this window) had that ability.
Also, Mason doesn't mess about with the ball if he doesn't have time. He'll happily hoof it up when needs be and that will also go against his stats.
If, however, you're not working off stats but purely from your own impression of the lad from watching him, then I would seriously question either your eyesight or your judgment mate. What I see is a very composed footballer, somebody who is happy to have the ball at his feet, likes to play the game on the front foot, get's his head up and looks to play forward, not sideways.
Don't get me wrong, he has his faults. His headed clearances are poor. His positioning at times is out and he also is guilty at times of switching off/ball watching. But I would not include passing ability in his list of faults.