The main difference is the money and the competitiveness between the leagues. London comes third.
As for the transfer if it happens... its somehting like a signature and a statment from Chelsea & Abramovic... the overpaying is hilarious, but its much needed. They havent invested big lately. so this is their chance to do it. The trade will help them to keep key players and sign them to new deals.
I dont think Juventus will change or downgrade, the core of defenders they have will continue to dominate, and im sure your board can invest 60+ mil pounds for some nice signings, and
be top candidates for the CL again next year.