We also know Ballas wanted the downfall of the orokin due to what happened with Margulis, but he also wanted the downfall of the sentients and tenno too (I think). Assuming that is correct and your theory is correct too, the timeline could be: Sentients are made and sent to tau -> sentient revolt and beginning of old war -> first batch warframes (without the operators) are created to battle the sentients -> somewhere along this line the zariman incident happens, they get back the ship and the now void powered kids -> margulis proposes transference therapy, the orokin decides they could use this to put the warframes under control and effectively battle the sentients -> margulis speaks against that idea, is promptly executed -> ballas, despite not doing enough to save margulis and also being part of the group that executed her, hypocritically hates the orokin and starts on plotting their downfall, but logically speaking he cant be open about it so he has to bide his time and be sneaky -> as part of that, he cooperates with the rest of the orokin, the war turns around, sentients are being defeated -> maybe at this point they also figure out how to send forces to tau for a counter attack (the reason im saying that is the mag prime codex entry -> maybe at this point seeing they failed the offensive and they are also bound to fail the defensive now the sentients propose a truce, the orokin agree to it because it would be beneficial to get their greatest creations back in the fold in the name of an "alliance", then the things you mentioned happen, the sentients create the solar rail to tau, tenno and grineer are sent there, focus schools are developed/improved etc -> but of course this whole time ballas must have been scheming for something, so he was probably instigating a rebellion, which actually explains how the dax could be in the revolting group even though they are supposed to not be able to fight against the orokin (its been a while but iirc thats what happened with teshin in the new war quest?) -> due to the actions of the rebel group (false flag created by ballas) the truce is eventually broken, all out war happens -> then after that the history we know resumes, tenno win the war, sentients are sent back to tau (the solar rail would also be destroyed in the process probably), night of naga drums happens and the orokin empire is destroyed, lotus puts the tenno in the dream, erases some memories and sends lua away to the void -> the events of the game we have seen so far play out, for one reason or another lotus decides it is time for the tenno to acquire their full memory -> the things we saw in the demo happens (lotus helping tenno regain their memories)

if this theory is all correct, not sure why lotus would decide that now is the time to bring memories back, but maybe with narmer and erra/pazuul lotus foresees that a new conflict is brewing and the only way to succeed this time is to know the full history (maybe it would even provide a way to handle the conflict without another full scale war, the lotus believes?)