I'm trash at posting so forgive for quoting the entire thing.
I very much agree with you on everything but the splitting part.
I saw it more as Uther bringing Sylvanas into a memory of his own (and therefore talking through his past self) before "splitting" from the memory of himself to show her just how different he is (which somehow counters her "you wouldn't know man". line)
Seeing as the split Uther had the model and armor of current, merged Uther and not the dark purple of Forsworn Uther pre-merging I think that's more the case.
Still, shame that the ruthless manipulator Sylvanas I liked from WC3 until Legion is nullified now (: