There are some great players in the league. But very few would improve the side, how it's playing at the moment. There isn't anyone in the league I'd have before KDB, Silva and Sane.
Keepers - you could argue that De Gea, Courtois, Lloris, et al but none will be able to ping the passes 50 yards like what we currently have.
Defenders - I think you'd have to go some to get better than Stones at the minute. I wasn't Walker's biggest fan but he is exactly the right player for us. If Kompany is fit there isn't a better CB then him in the world. I haven't seen enough of Mendy and can't fault Delph but perhaps a Rose.
Midfield - There is no one in this league better than KDB and Sliva. Could you put a Kante in instead of Dinho, maybe.
Up front - Sane is going to be a world superstar and is Jesus. You could find a place for Kane if you really had to but, again, only if you had to.