Greatness aside, Fallout 2 was full of stupid things, and the talking Deathclaws were one of them.
Super Mutant Melchior in the military base, the optional "boss fight" in the second game. A fun fight, but still super stupid.
Fire geckos lacking any explanation for their existence, it's like some developer was into D&D and decided to include "dragons" in the sequel, at least in my opinion this is one of the critters that belong somewhere else, not Fallout 2. If they could only be found in the special encounter where the MC is ambushed by a trillion of wild Geckos, okay, as those encounters shouldn't be taken seriously by the player base.
The Brotherhood of Steel having interest in Vertibirds, but ignoring the Hubologists Shuttle. Yeah, there's some flaws in their spaceplane, a number of things the scientists didn't take into account, resulting in bad endings for their faction, that you can find on the web. Even so, you'd think they'd at least want to steal components from the spaceplane, or something.
Ghost in The Den, one of the quest givers in the town. You can kill a person that is already dead: You can explode her with Plasma grenades, since she's not immune to plasma.
Talking spore plant, in Broken Hills.
Fallout 2 is still my favorite one,
despite these things.