I mean, yeah, it is dumb. But I think the idea is that the bad guys are defeated by the people they’ve used and abused. Rey healing the serpent inspired BB-8 to give some of his energy to D-O, and that act of kindness gave the heroes an unexpected advantage.
Honestly, I’d love to see someone replace D-O’s human (JJ Abrams) voice with some glitchy beeps and boops like a normal astromech droid would make. Especially when the droid just says stuff like, “sad” and “happy”. It’s not endearing.
That would be adorable - like you said, it’s not endearing for D-O to tell us that 3PO “dying” is “sad.” It’s like a laugh track in a comedy, but somehow even more inauthentic.
You know, thinking about it some more, I don’t necessarily hate D-O having information on Exegol; I hate how unearned the information is. They’re just moping around, and then D-O, off-screen, tells Finn, “By the way, I have all of this super valuable information, if you want it!” Maybe if R2 or BB-8 or someone had to repair D-O to unlock the information, it would explain why they’re just discovering it now. Heck, if Finn had just realized on his own that D-O might have this information saved, it would at least feel like something the heroes achieved, rather than something they were handed by the screenwriters.
EDIT: God, they can’t even be bothered to build up to the reveal at all. The hanging question is Finn asking D-O “What’s your name?” And then he goes running to tell Poe that D-O is the answer to their prayers. Why couldn’t he ask a question that’s relevant to Exegol?