At their best at Chelsea, Ruben is miles above Barkley. RLC looked like he was on his his way to be a special player. He was a big reason why we finished strong under Sarri, going to Europa final and capturing 3rd place. You know a player is class when others are playing well, and he is able to stand out. Barkley at his best looked like a depth player at Chelsea.
Naturally some players are better fit for some managers; Kovacic and Zouma were beneficiaries from Lampard management and tactics, while Rudigar, AC, and Jorginho. You could also make an argument about Kante too, his performances were day and night under Tuchel and Lampard. Maybe RLC benefits the same way under Tuchel. It is worth exploring in pre season.