To be precise we didnt gotten his fruits name yet and class of it.
He was referred to as Stone Assimilation man same as Trebol was referred to as Muscus Man and Doffy as String Man. Trebol being Muscus Man still ended up as Paramecia.
I think that difference between Vergo vs Smoker fight and Pica vs anybody was that Smoker was amplifying his own body volume by spreading his smoke, his element.
I mean like manipulating his smoke volume in the air while Pica being a logia could so same thing while inside stone.
So by amplifying his body volume he was able to take control over big mass of stone and for example creating gigantic Pica golem-like form.
Also amplifying his volume in scene on picture above made him bigger target for haki user like Zoro(goes well with Vergo words) - so Pica being logia would make a lot of sense.
Magellan traveled through slime-like poison he created so I see those 2 differently.
It would make most sense if Pica is a logia and he uses his body size change inside of stone while assimilating it and manipulating.
What is the common factor to every logia user so far? If i suggested element, would you disagree? i would not say string and mucus are say in the same field of matter as ice, fire, sand,magma, light, mud or swamp, smoke, snow, darkness. I concur on the fact of solids like ice and sand as logia, but they could claim to be part of what is natural and fundamental interms of what akesthe world and universe, there is earth represented by sand and swamp, water, ice and snow, darkness and light , magma too earth. But mucus is not something that would be as natural as ice. Stone assimilation.
So pica was manipulating his volume while inside stone? That seems very sophisticated. There is logic behind what you say, however based on what we know as of now, is'nt there a vast difference between how we saw logia put themselves back together and pica way. Lets say the conclusion to his and zoro battle, would a logia at that instance be left with just his haki and luck that the opponent own haki is weaker or like kuzan evade that blow, by using the stone he should be able to form without the presence of any stone. The way it looked to me, was zoro tactics was get him out off and out of any and all contact wih stone, now of he was able to manipulate his volume inside of the golem with his stone, that his, his actual bpdy should in essence be able to take advantage of his element as means of defence? Even against haki.
Ps great point on magellan. You got counters to them all. I wonder if you are into law or something.