We have good example with Kuina, now we are far from understanding fact how Luffy will be able defeat Younko. But Gorosei has to be on different lvl, so I'm not sure.
But again, I just
showed way how this
could
became true, case if Gorosei is 1000 years old, than he is real WSS of all time, and if Zoro would be able defeat him, than yes, he will became WSS of all time, your right.