Looking at it another way, he has fallen out with a manager who has already fallen out with another player and only been at the club for 9 months.
My point being is we do not know exactly what has gone on. who is to blame (if anyone) etc.
My take on this is he’s a young keeper, with a lot of potential, who has lost his way a bit. I think a fresh start somewhere else will benefit both sides. I wish him well and hope he is a huge success wherever this may be.
Same could be levelled at Trossard? He lost all interest after the WC, argued with team mates, fell out with RDZ and then stropped off to Belgium. All very disruptive. Why did Arsenal bother?
Lots of things Chelsea do seem pretty stupid these days. And one thing they are excellent at is spending big. I would not discount the transfer for this reason I have highlighted.