Overall, fuji hasn't shown to be all that impressive, barring the fact that he is an admiral replacement of aokiji.
Your argument is that because zoro would have to wait another arc to fight fuji, therefore he cannot extreme diff fuji is invalid. The reason is that luffy will also not meet akainu until another arc at least, but akainu will need to extreme diff current luffy, assuming luffy will end up soloing kaido. The other flaw with your argument is that zoro might not even fight fuji at the end.
You have to look at the facts. Zoro has adv CoC now, he scarred kaido without even awakening his adv CoC fully.
Fuji might or might not even be able to scar kaido for all we know.
To now and say that zoro won't push fuji past high-diff based on the sheer evidence we see would be completely biased.