I also agree to the Giants theory.
As I have stated before in another thread, while the Giants we have seen so far have not had a great battle record (Oars, Oars Jr, Jaguar, Droggy, etc), we have not witnessed neither a Giant Devil Fruit User, a GOOD giant haki user, or a 6 arts Giant user, in all of 800+ Chapters.
Think about it, if a Giant was capable of using Soru (or a equivalent), had a good df, like say, Akainu´s, plus a powerfull amount of haki on top of the common bulk,size, and power of a Giant, how unstopable would he/she be?
Even the aformentioned bad record of the giants, lets look at it shall we?
-Oars was as dumb as Luffy while being controled by a deranged Moria. Still required ALL of the strawhats (pre timeskip) + Nightmare Luffy to defeat, a feat that no enemy has yet to need to be defeated so far. (More on this below, for the sake of order)
-Oars Jr teared his way all through the marine forces, getting the closest any of the WB pirates, even Marco, had from reaching Ace. And that was tanking hits from pretty much all of the Shichibukai present there.
-Hajrudin took on freaking 10,000 tons. And that was after being exhausted from fighting in the coliseu, decked by Luffy, being turned into a toy, and running around dressrosa.
All of those required (at the time of writing the story. I am sure most if not all of the current SH could solo Oars [no moria] now) absurd power level conditions to be beaten: DF users, Admirals, Another Giants, Plot convinence, being exhausted, etc.
We still have not seen ANYTHING close to the Giants full potential.
(On the "required all SH" to beat him thing on Oars, I am trying to say is that while Luffy and the others right now could beat most of pre-time skip by themselfes, Oars was a situation that required all of their manpower at the time, which is still a lot. Sure, other characters that prob won´t need all the SH grouping, like say Luffy vs Akainu/Teach are LEAGUES above Oars, but they still don´t need the full might of the SH to bring them down. Dunno if I sound too confusing with this argument)