We have Roger's words, which are > Kaido's words (silhouette in this case).
On the other hand, yes it's about pirates. Pirates are the people fighting for making their dream true in this manga, it's a manga about pirates. Pirates are Kaido's rivals, and Luffy's. Make a list of the arc bosses and see the number of marines vs the number of pirates and you'll get it.
And all those represented there are goals or rivals of Kaido. Garp has nothing to do with Kaido. Garp is in Linlin's generation while Kaido is in the next one.