I'll just copy-paste what i posted on the chapter thread
Early days and till it is somewhat confirmed by the VIZ fans but still, we finally get a glimmer as to why the Calamities and Tobi Roppo could be loyal to Kaidou. Before this it seemed that being under anyone else ( any other Yonkou) would be preferable since staying with Kaidou leaves one vulnerable to his drunken whims and a crew hierarchy where everyone has to look for out for themselves and keep getting stronger or else.
Now, it looks like Kaidou on some level does appreciate the worth of his subordinates and won't just discard them aside. Him waiting while Jack and his team faced off against the Sulong Minks could be read as him being arrogant and letting Jack and co. weaken his enemies OR it could also be read as him in a way respecting and trusting that his Calamity Jack was able to handle the minks and leaving him to deal with it. Until he could not anymore.
And I just get the feeling that Oda is rather fond of the little failure of a fuzzball that is Jack the Drought. Him going up against the odds and getting beat down again and again and yet keeps on grinding away, kinda appeals to Oda I think. He isn't going to be one-shotting Admirals or the like, but Oda gives him manly losses without making him lose face and his final defeat will be a respectable one.
On top of that, we really haven't seen his Fishman based powers either. I'm sure that's how he sank two out of 4 navy escort ships under the watch of Sengoku, Fujitora and Tsuru, and not by lobbing cannonballs while the latter three sat back and enjoyed the show.
i really hope king and queen are as loyal as him
Queen's 'overdramaticness' aside, he was pretty loyal to Kaidou back in Udon. While the fodders were already thinking of cutting deals and switching sides to Big Mom, Queen got up and proclaimed ,"This is Kaidou's turf!" and thought up a countermeasure that against all odds, succeeded in capturing BM and sparing Udon from destruction.
Jack's backstory could be interesting indeed. Out of all the Calamities he's been featured the longest. And as others have pointed out, it feels like Jack could be Kaidou's spiritual successor in some manner. Even his silhouette resembles Kaidou the most out of the Calamities.