I think Top 5 is a stretch when we're talking all time:
Dre
RZA
Marley
Larry Smith
Premo
^^^ it's tough to break through that tier. You have Dr. Dre pretty much with the NWA era, D.O.C.'s Nobody Does It Better, Chronic, Doggystyle, the work on All Eyez On Me, the work with Eminem, Chronic 2001, 50's GRODT, Game's Documentary, etc.
RZA has Wu as a group and their solo work. Has there been a greater 1 year run for a producer in Hip Hop than the one RZA had in 1995 with OB4CL, Liquid Swords, and Return to the 36 Chambers?
Marley is so much of an architecht. There's what he did on Paid In Full, Big Daddy Kane's debut, LL's Mama Said Knock You Out, there's "The Symphony" and I know I'm forgetting some.
Larry Smith off the Run DMC and Whodini music alone
Premo was a huge part of the debuts of Nas, Biggie, and Jay. There's the production for those artists beyond their debuts that is also legendary. Then there's the work with Jeru, the Gangstarr albums, Group Home.