They retold some things via the Echo, or remade it as dungeons, trials and raids. And not everything from 1.0 is still lore. They salvaged what they could, as much as possible. They can explain some it away by saying NPCs thought this or that, but the truth was something else, because in real life people can think things when something else is in fact true.

The issue from it to begin with was that it was all bland and making new story was difficult for them with all the issues as well. When Yoshi-P took over the story was mostly keeping people entertained with fights or content (which was recreated as dungeons, trials and raids in ARR), or as something to build up to ARR and then those events were retold with the Echo where relevant.

People in ARR are still largely doing what they were doing in 1.0 despite it having been 5 years. It could make you question why Gaius hadn't gone the rest of the way and conquered Eorzea in that time while they were weak, but it could be argued that the calamity also weakened the garleans somehow. It could also make you question why these under-developed scions still looked so young and only developed after you came into their life. You could wonder how you end up re-fighting all these battles that already happened in 1.0.

The whole point of it really is that you aren't meant to have needed to have played 1.0 to understand ARR and they redid as many things from it as they could. You can find it on youtube though.