Won't make any judgements on his character or call him all the names under the sun like some have done, as I don't know him and can't be sure on what exactly happened behind-the-scenes. There must be all sorts that goes on and things that are said that we will never know about, and I know from plenty of experience that these kinds of incidents are almost never as black and white or "goodie and baddie" as they might seem, so I won't judge a guy based on rumours and one-offs.
All I do know about Cancelo is that he's a talented lad who clearly has quite a sensitive side and can be easily angry with himself or others if things don't go as he hoped. He's also been through a couple of traumatic incidents that I'm glad I can't even imagine, like the accident that killed his mother. Surely that affected his moods, his mental health, and perhaps his career decisions and teammate relationships. I don't know. So I won't say.
I'll just say I'm sad to see him go. I support all of our players (with a couple of extreme exceptions) and root for them all the time they're with us, and I still hold a soft spot for many after they've gone, too (not Milner, he can f*** off). So I hope he does fine over there, although I won't exactly follow him with the same level of fondness as the likes of Silva and Dzeko.
In his time with us, Joao did a lot of good things. He was a big part in us winning the league last year, in particular, and played his part in our other successes. I think it's foolish to say otherwise, and I won't write off or discredit a player's contributions just because they've left the club, even if it is an acrimonious departure.
I do agree that his defensive work wasn't the best, but it was far from terrible, either, and he has rightfully been classed as one of the top full backs in the game. He also adapted very well to Pep's tactics, and the way he played the inside WB role and drifted into midfield and onto the wing in certain games last year - effectively playing 3/4 different roles in a single match - was something to behold. In spite of his faults, he's been a great player to watch (obviously not in every game he played, but still a fair number of them).
Losing an in-form Cancelo makes the squad significantly weaker. But losing an out-of-form Cancelo who is potentially causing issues off-the-pitch might not be so bad. We're still lacking in the full back spots and I think we'll have a hard time competing on three fronts now (unless a last-minute LB arrives), but always have faith in Pep to figure things out.