"The design has neither guiding intelligence nor coherent moral imperative behind it…."
It's not an odd intelligence. It's not an intelligence at all. And no, it's not the Maidens future-selves telling their present-selves what to do. The Maidens are subservient to it.
It's also not the ST's plans for the campaign, because the ST's plans for the campaign might include something like an invasion of aliens from beyond samsara that the Maidens can't predict and who, as soon as they show up, start to make the Maidens' prophecies demonstrably false in short order when previously they had always been true in some sense.
Yes, in many ways, but this is not the problem.
A child could never be his mother's father. In this sense, causality is still valid and allows us to leeway to discuss a "timeline" - before and after.
The samsara just say "Whatever comes after this can only be in this specific way and in no other way" - hence, free will is gone. No matter the will, it must act in accordence with the samsara.
No, you misunderstand.
Time as we perceive it — as distinct from space — is an illusion. We perceive time flowing, but time doesn't flow, not really. Everything is frozen in a giant four-dimensional lattice, of which we can only see parts. At any given point along the time-axis of that lattice, we can only see other parts of that lattice occupying the same point on the time-axis that we currently occupy. (This is not actually true; in fact we can only see slightly behind, and further behind as you go further out — this is stuff to do with light cones and things.) Things like movement and change are illusions.
Samsara is a fantasy metaphor for that lattice.
As nearly as we can tell, this is how the real world works. You object to samsara on the grounds that it removes moral agency from characters in the setting by making everything predetermined, but if it has moral bearing on Creation, it has the same moral bearing on Earth. Clearly, here on Earth, you believe that what we do matters, at least to some extent, so why should samsara's existence in Creation impact your opinion on whether what people in Creation do matters?
Samsara exists for a lot of reasons, but yes, one of the reasons it exists is to challenge your opinions about free will in the real world. Exalted is full of that shit. It's an iconoclastic game.
In practical terms, the existence of samsara in Creation has exactly as much bearing on anything as philosophical wanking over whether free will actually exists or not has bearing on our lives in real life.
Yeah, if your ST is using samsara as an excuse to have the Maidens tell the PCs what they're going to do, and then telling you, the player, out of character, that you have to have your character act the way the Maiden said he would because that's how samsara works, then your ST is being a jerk and needs to be slapped. (Or metaphorically slapped, at least. I don't actually advocate physical violence in those situations except as hyperbole.) That's not what samsara is for.
Samsara is indeed meant to be a background device, to explain the mechanism behind Of Things Desired And Feared and the backwards-traveling-demon-summons and why the Maidens basically just do whatever the hell the ST wants them to do.
(Well, that and raise interesting questions vis-a-vis the coherence of "free will" as a concept.)