I guess it is a bit uninteresting, but it was necessary to invest us in Kuma for whatever Oda has in store for him when he lands on Egghead. Just think about how you viewed Kuma before the flashback and how you view him now, totally different. But yeah I also think he overdid it with Kuma, he could give him a little less tragedy and make it shorter but I guess there's a reason if we're on chapter 1099.