not fully complete, but it should give a rough idea of what is in it
#transcript disc 5
small cosmos
small cosmos
lunar tide
Segment 5: ancient city under attack by an endersent, center structure is activated, endersent is hurt and the warden is summoned.
W
eternal bough
cool
small cosmos
Building upon this, it's evident that there was some fight with endersent in the past. This goes towards two options: Either the inhabitants of the cities fought them, or the illagers exploring the city did. The first hypothesis would lead to the conclusion that there was knowledge of the end and cc a very long time ago, which somehow started cc in the overworld. In this case, I find it likely that the ancient cities were not constructued for enchanting, but were more like military bases due to the presence of barracks, likely constructed there to fight the endersent. The city center would then have a purpose of hurting the endersent, which we hear it do in disc 5. This does explain why there is such good loot there, as it makes sense that the best resources would be used to fight a world-ending threat. This war on the endersent was eventually won, as the overworld still exists and the story was forgotten until the illagers stumbled upon the ruins. I figure it could be possible that the Ender days were somehow started by this discovery and that it was the first thing that taught the illagers about the end, but that part's just speculation. The second hypothesis would likely go along with retro's theory and mean that there was a war on the endersent by the illagers, which i figure could have happened shortly after the end of the ender days as the orb betrayed johan.
I favour hypothesis 1, due to the fact that if disc 5 was recorded by an illager it would likely be found in other illager structures, not just the ruins of the ancient cities, besides having the longest time between the endersent fight and mc/mcd. This part is likely important due to the Illagers likely not taking on archie with the orb as their new ruler when at least some of them should remember that it almost destroyed the world and that there were wars waged to fight it. The fight happening during the ancient city days creates a much longer time passed, and so it is a lot more reasonable that this memory has changed drastically, if not gone entirely. Lastly, I find it harder to believe that the city center hurt the endersent if it was simply a catalyst as retro explained. Occam's razor would dictate that the center was made for hurting the endersent, as the only working example of a catalyst in the world, the sculk catalyst, does no direct harm to anything besides blocks.