And in the next sentence Hythlo states "that another half sacrificed themselves" sounding to me that it was quite near half the people. Even in your pie chart its quite near the half. So I am not really sure why we are talking about semnatics here? Hythlo himself probably has not counted the amount of people either.
My whole point was that Hydealyn always had way less amount of aether to be reproduced which is why she needed to split him (and no that makes him not death). We only know that one member (which is probably the old us) went away. There is a high chance that the very same person did a part in summoning Hydealyn (and its the theory I follow) but for all we know they could have been against that too. There is also no ingame text saying that she needed more fuel afterwards and Elidibus mentions summoners as in more than one.
My whole answer to you was just because you said that the first sacrifice was only there to fuel him and the rest was for his actions. With Hythlo in your screenshots says that it has not happened. He already stopped the calamity with the first round of sacrifice.
Also it may be true that they are not there or it could simply be that Zodiark somehow sent them in the rift to save them when he noticed that he was losing. There are many possiblities here.
About the OP: The cloud in the sky could simply be the door where the meteorits came from. We know from the dungeon that the Ancient ones created their own nightmares and we see them spawn in just like Ascians spawn into the room. We also know that the sound came from the earth itself, it did not start from the sky. So this violett cloud could simply be created by the fears of a bunch of ancient ones that even the sky would turn against them.
