I'm not sure if somebody mention this before,or maybe I'm a bit farfetched….
But in my opinion,I think there's big purpose in this mini arc that would contribute to the whole storyline....Come on,most mini-arc contribute or are foreshadow of what is going to happen next....the Jaya Arc,there's Doflamingo & his new era,the Dave Jones Arc show us the immense power of one of the three admirals.Ao kiji could easily owned them at that time.
So this is what I think make this arc significant....
The world government may be funding Dr Hogback's research thru Gecko moria,or the WG may send Gecko Moria to defend Dr Hogback's research.
In turn Dr Hogback may give a vial to Gecko Moria that will make his long,lost love ressurect OR a vial of immortality.Not sure which one…yeah if Dr Hogback were to create a vial of immortality(or maybe he already have)...think about the old 5 elderly star...or maybe he already had and only make 6 vials,one for himself and the other 5 for the 5 elder stars.
And oh,the dark art of ressurection is an abomination.Think bear n bible.
Not surprise if he make an appereance,then Luffy kill 2 birds with one stone.(or maybe one of them joining the strawhat).Next arc,I think he will defeat (or maybe join again,I swear one of the shichibukai will ended up becoming a strawhat) Jinbei.By then,the WG will take notice and realise they're short of 3 shichibukai.By then,only 3 seats are filled (Doflamingo,Hawkeye and a very powerful x-pirate).
From then on,I think the WG will dissolve the shichibukai since 4 had fallen under relatively short time.