Haki can be broken sure, but we have never seen hardened armament haki broken without haki. And yes we can use part 1 no haki to compare to part 2, its part of the story you gotta deal with it.Zoro had to cut stone fighting Pica, Zoro had cut stone before facing Oz yet hiss sword attacks against Oz were hardly deep cuts, even that raven attack which looks like it would shred a normal person. Also I don't care about Vergo or his ranking in regard to Pica so why even bring that up, it feels like you're beginning to bring other things into this issue.
The Earth we live on is irrelevant in a manga, buddy, Oda has shown us islands that have no rock.
Do you remember how big Oz was? He was 4 times the size of an average giant who are already 15 meters or so tall(the 15th anniversary "dive to grand world says over 15 but let's say 15) that's 180 feet.
People can we stop with the (insert part 1 character here) doesn't have haki because haki wasn't explained during his time in the manga. If Oda had intro'd armament Haki in chap 1 I'd say very valid point but Oda had never hinted at the concept before the fight with Oz so why would he have Oz show it? Also Oz had Luffy's shadow which gives the body the abilities of the original and Luffy didn't have Haki then, I know a lot of people hate hypothetical's but we actually have no idea what Oz himself was capable of, we only saw him with Luffy's skill and mind state being controlled by Moriah he had no free will or sense of self in that fight and we all know it to be true.
As for Oz's strength, Giants are naturally stronger than a normal sized human and then Oz is four times that gap so Oz is at least 8 times as strong as a good fighter of human size. I'd say that lends a serious hand at breaking an opponents haki, you'd have to have some of the densest Haki imaginable and just because you can coat your whole body doesn't mean it will be dense enough. Also his strength was said to be able to move continents so what's an island gonna do to someone who can move a whole continent?
I've been wondering something about Haki too, say you have 100% Haki in a person. They can use that 100% all in one location but when they disperse it to multiple areas simultaneously is it still 100%at all those spots? Logic would say no, fanyboyism probably says yes. I would think it decreases in density or impactfulness the more it's spread, so instead of having 100% effect on a hand you get 60-70% everywhere.
Luffy broke through Boa Marigolds using gear 2 attacks, which I'm sure you'll come back against with Oz doesn't have, Luffy's main character, Gear 2 isn't pure physical power yada yada. My point is still true that Haki can be broken without Haki.
i am not sure how fullbody haki works, but seing as how its is still hardened it is greater than any armament haki seen in part 1. BTW dead Oz is clearly not strong enough to move a continent and I assume that is what would be fighting pica not alive oz.