Williamson has a team that just might surpass some of what FLeming achieved (with a far more limited team). But he hasn't actually done much apart from win at home yet. I suppose ODI WC Final is an achievement of sorts but you don't hear Pakistan claiming '99 as some huge achievement.
Williamson has a far, far more talented team. A far superior batting lineup & an atg (for NZ) pace attack. If he doesn't achieve what Fleming did, he should be rated poorly as a leader.
What Kane needs to do to even get close: draw in Oz, draw in India, win in England. None of these are easy, for any team. He has the team to achieve this in Oz & England. He lacks the bowlers to win a Test in India, so it'll have to be a batathon.
How could Kane surpass FLeming:
a) Win World Test Championship.
b) Win tours in SENA countries. Needs series win in at least one, draws in the rest sometime over the course of his captaincy.
c) Achieve something in India. If he can do this, without spin resources he will be regarded as a great captain because he'll need to coax perfomances out of mediocre spinners or captain his quicks to perform in places hostile to them.
HOW is he supposed to do this? Not sure NZ aren't booked to play another significant Test tour until May 2022, England... Only other significant Test tour they have his Pakistan October 22... then nothing much until the FTP runs out in 2023...
From a NZ point of view it is essential they win that WTC for the status & series hype so that India, Oz , England will invite them quickly in 2023/2024 while they still have this good team.