...I can't talk about the first and third one but do you actually want me to give examples of Millie being dumb and not a bitch? because there are some that come to mind, like when she tweeted her phone password while asleep and panicked when chat asked what those numbers meant (EDIT: found it, it's on her Warioware stream from december at 5:14:04), or when she forgot/ignored to go to the dentist to fix her impacted tooth for like 3 or 4 weeks, or when she took an electric kettle to her camping trip in the outdoors, or how she seems to have the tendency to ignore when she is sick/injured only to make that sickness/injury worse by overexerting, or how she has several times eaten something she knows will be bad for her stomach but doing it anyways, etc.
But the first example that comes to mind is the infamous stream where she defends Niji, because everyone forgets the context. I'll copy and paste what I wrote about it some months ago (IIRC it was The Karaoke Chilla's game):
And if you want more examples I'm sure there are clips of her being dumb, so yeah I'm willing to believe she's dumb and not malicious, like her lore and emotes are not lying when it says she has -3 intelligence, she's actually like that.