Okay, what is invalid about Celestia's show of immaturity? If you mean her being freaked out by Daybreaker then I'd chalk that up to her being not simply a creation of Starlight's dream but also a product of Celestia's own mind mixed in with Starlight's dream. She just seemed to know way too much about Celestia to have been made by Starlight.And as for what they learned about each other before becoming rulers, what does that have to do with anything when the conflict was about what they do as rulers and how it effects their relationship?And apparently the staff have said the Journal is still canon, though it requires one to interpret Celestia and Luna's words very literally (namely that they were born before Equestria was founded, hence why Celestia says Equestria has never seen a alicorn be born, that the duo left the other alicorns when they were still young, and that this combined with it being over a 1,000 years ago means they don't know anything about newborn alicorns).