Definitely Kean and Huijsen have been better than Kelley and Vla. It's quite obvious.
Kean scored zero his last season with Juve. Vlahovic despite on and off role and overall dissapointing season, finished as our top scorer.
If Vlahovic was back in Viola he would score well too. There's different levels to this.
I only agree with Huijsen being better then Kelly too. Rest not so much. Miretti was Tuz whipping boy and super hated around here despite his young age. Koop was best mid serie A with Hakan.
Soule is a Roma bench player, Luiz was top 5 midfielder in EPL over the years before he joined us.
You need to ask yourself why everyone performs worse in Juventus? That's a more pressing matter then direct comparisons.