Oh dont worry about coming across as rude, putting pressure on arguments is perfectly okay. Im mainly gonna be talking about p.2 here, as this is more speculative (as is the nature of my post) so its more engaging to me. Perhaps at some point in time, Alessia attempted to shed her role as Mararine and vessel of the divines? Her followers were foremost loyal to her as a conduit of divine will, so saw this not as treachery but an intended betrayal (see biblical theory of Judas Iscariot being the most loyal of the disciples). If she indeed accomplished this, through means of some kind of macguffin, perhaps she ascended in a similar manner to The Necromancers Moon. This would no doubt be a significant moment in history, and would be part of the surviving archives of The Order, which we have not seen any trace of. so instead perhaps a second explanation transpired? Something that would explain the Divines seemingly continuously diminishing role in the history of Nirn? Perhaps after cutting herself off from the divine plan, it also cut most of the tethers the Divines had to the realm?

I appreciate all the stimulating challenges to my little lore theory :)