The world will be in turmoil after the end of the shichibukai and pretty much the Yonko system too, so letting some substantial time go by so that the consequences of this event can happen worldwide makes sense to me, not to mention that Wano marks the end of most of the plot lines that have been built since the end of the timeskip so having another one to establish the end of this section of the story and the beggining of the next and final one makes sense to me as well

especially because it would be dumb to have a pirate king crew of only 10(hopefully 11) people and 6 of them dont know any form of haki