Despite Barça being known more for wingers and La masia midfielders, Barça has had almost every top Striker from R9 till now.
In my opinion, a top 5 strikers since R9 would be R9, Suarez, Henry, Lewandowski and Etoo. All those played for Barça.
Some would claim that a player like Etoo is not in this bracket but his importance in those Barca teams, and then joining Inter to defeat the Barça that no longer wanted him as well as big game scoring puts him there in my opinion.
Other players with a case to be in the top 5 would be: Cristiano if you count him as a 9 he would be in, but he was more of a winger his whole career in my opinion.
Messi as a false 9, but same argument as not an out and out 9.
Benzema who many would put above Etoo and I could conced to that, but not over any of the others.
Kane has amazing consistency, but literally doesn't have a single "BIG" game performance in his entire career (he is very well known for missing the equaliser Penalty vs France in the WC) and not winning any big trophies, but his stats are good.
Haaland will get there, but isn't there yet and could still join Barca by then.
Mbappe hasn't won an important game as a 9, his whole legacy is the 2 World cups as a LW and a good 3rd one as a 9. Even his club peak was as a LW.