I think Shirahoshi is interesting but that's it.
That said, the greatest thing about this flashback is both Fisher Tiger and how it has managed to humanize (lol) one of the most ferocious villains in the series. I actually REALLY feel for Arlong now after this flashback. I mean, I did during the Sabaody arc, but now I can't help but really like him and how he constantly hovers over a vast array of greys. I mean, sure, what he did was unforgivable. But the more you learn about his history, the more you kinda think he was a man (lol) who suffered much and ended up going too damn far.
This arc also has made me REALLY like Jimbei.
I don't understand how you can say Otohime is more interesting than Fisher, but whatever.