Astle's barely anything less than Fleming. I'd say Oram is potentially a better batsman than either, but just hasn't got the results in ODIs, probably because he needs to play up the order and away from the death. Fulton's another good one as we're seeing here. One of these two should be opening the batting instead of McCullum.
The full compliment of NZ's team is an interesting affair, the whole is greater than the sum of its parts. Most players can bat adequately and several offer bowling choices, leading to option after option in the field and the ability to carry the scoring beyond what is reasonable for conventional teams.