If we're looking at all-rounders as the greatest cricketers (in terms of contribution to their teams), I think it boils down to a select few.
The following players would have been selected for their national teams as either batsmen OR bowlers (or wicketkeepers):
Miller, Sobers, Jack Gregory, Botham, Gilchrist, Les Ames, Flintoff (briefly), Kapil Dev (probably would have been selected as a specialist bat even if he didn't bowl)
Players capable of batting top 6 and either being one of the four main bowlers, or being the wicketkeeper, have been pretty rare.
The following players would have definitely been picked for their dominant skill, but it's questionable whether they'd have been picked for their secondary skill:
Imran, Hadlee, Davidson, Kallis, Flower, Lindwall, Benaud, Wasim
Any I've forgotten?