I don't think we have any. My point is less that she is specifically for sure a primal and more that we're operating on faith no differently than the worshipers of Ifrit, Titan, Garuda, Leviathan, Ramuh, Bismarck, or Ravana. The only difference between us and them is that no "more enlightened" beings have come along to point out that... oh, wait. I think I've figured out what's going on. The Ascians are foils for the Warriors of Light. If it's cool for us to go around stepping on lesser gods that ours might live, how is that any different from the Ascians? And please don't pretend we haven't already justified some degree of wholesale slaughter as a tragic necessity.
Probably both. I was more objecting to the conflation of Hydaelyn and the Lifestream, since aside from both being billed as the source of all life, they operate very differently. The Lifestream is nature itself, a great unknowable that we nonetheless need to survive. Hydaelyn, on the other hand, is a personified entity with a benevolent will. A "god," if you will. They aren't the same thing. The Lifestream, much like nature, will preserve itself, and we can either work with or against it at our peril. Hydaelyn, on the other hand, comes bundled with an entire code of conduct that happens to include the suppression of false gods to ensure her continued existence. That's religion, not existence itself.
Honestly, I prefer how Dissidia worked out. Rather than the heroes endlessly sacrificing themselves to save Cosmos, the so-called "king piece" Cosmos surprised everyone by exemplifying the Light's virtues herself, in a move that ultimately dethroned both Chaos and Cosmos. If Hydaelyn truly cares for all her children, the discussion is moot because she wouldn't demand anything of Minfilia.
To get this dead horse galloping in a different direction, what if Minfilia is trying to sacrifice herself against Hydaelyn's wishes? As in, the mothercrystal is ready to let herself fade away in a bid to save her children, but Minfilia is trying to keep her from doing it, at her own expense?