It's football not math
You probably think Salah is a better foward than Drogba was
Just off the top of my head Willian carried Chelsea when we played Tottenham and there are several other games when he was the best man on the pitch or close to it
There are also games when he was like a ghost, like I said Willian's problem is consistency, on a good day he's a first rate player
There's a reason why Barcelona was bidding for him last season
Willian has 3 good games a season and that Spurs game just happened to be one of them. After that game he went a full TWO MONTHS without scoring or assisting a goal. Imagine having one of your most senior attackers going awol in the make or break period of the season.
He is an absolute fraud who lives off random games or moments like the Barcelona match from a few seasons ago.
Barcelona have bought badly for several years so it's absolutely fitting that their hierarchy wanted him.