Imo Oda messed a bit with this stuff. I mean first we have Marco gave that message to Neko for Luffy then it is simply resolved in nothing to make Marco suddenly join then there is this other weird turn where WB, who was the WSM, went against the WG to free Ace and actually the one scared was the navy but now Oda instead forget that in order to not let WB come to Wano. He builded all this arc with Oden and some of the new points he made just couldn't fit well with the old ones so he tried to fit the old and the new but of course problems like this occurred (it is like woth the nonsense powerlevel jump Croco had from Alabasta to Impel down/Marineford, the only fitting explanation would have been that Impel down was a better training point than even Udon, the bigger the prison the best your training).