And what is this new information that supposedly proves that the pillars of the earth are the Forgotten Ones?
There is none. The new information the Descent provided more so connects the Titans and the Pillars of the Earth to be the one and same. I think most people make the Forgotten Ones and Titans/Pillars of the Earth connection based on these facts;
1) The location of the Forgotten Ones were supposedly called the Abyss, located inside the Void. The Anvil of the Void already suggests that the place below the deep roads is infact the Void. The Descent DLC did nothing but strengthen this assumption, as the first region that we encounter below the deep roads where we first encounter the Sha Brytol is called the Forgotten Caverns. This particular part of the deep roads also just happens to be part of a place called the Uncharted Abyss! You gotta admit, that's very convinient!
2) Supposedly Andruil went to hunt the Forgotten Ones inside the Void. If the Void is infact the region below the deep roads, then that means that the Titans are infact the Forgotten Ones. Of course this assumption doesn't account for the fact that there might be other regions inside the Void, harbouring the Forgotten Ones.
3) Knowing how the Shaparate of the ancient dwarven thaigs erased all memories related to the Titans, the name just fits the Titans like a glove. They are the Forgotten Ones, because the very memory of them were erased from existence, causing them to become forgotten.
4) In DA2 inside the Primeval Thaig we find evidence of ancient dwarves worshipping their own pantheon of gods. Knowing the dwarves connection to the Titans, they are most likley what the ancient elven pantheon were to the present day elves. Considering how common conflict between dwarves and elves is in fantasy in general, I wouldn't be shocked if the Forgotten Ones and the Elven Pantheon painted each other as evil for the sole purpose that they were arch enemies? The following elven codex entry found in the Arbor Wilds seem to reinforce this;
"In this place we prepare to hunt the Pillars of the Earth. Their workers scurry, witless, soulless. This death will be a mercy. We will make the earth blossom with their passing".
5) Supposedly Andruil made armor out of the Void, which caused her to go insane. The Sha Brytol had their own skin turned into armor by fusing lyrium into it. Very convinient don't you think? And the Sha Brytol were no doubt insane, proving that regular lyrium can corrupt just as easily as red lyrium.
You gotta admit, there's some pretty convincing foreshadowing going on here. 
It's really hard not to draw a pretty strong comparison case between the Titans and the Forgotten Ones. Of course what neither of these hints help out with is to fit red lyrium and the blight into the picture. Nor do we know if Andruil's supposed armor were of regular- or red lyrium origin.