It seems to me that "vibe checks" for how smart a model feels are easily gameable by making it have a better personality.
My guess is that it's most of the reason Sonnet 3.5.1 was so beloved. Its personality was made much more appealing, compared to e. g. OpenAI's corporate drones. [...]
Deep Research was this for me, at first. Some of its summaries were just pleasant to read, they felt so information-dense and intelligent! Not like typical AI slop at all! But then it turned out most of it was just AI slop underneath anyway, and now my slop-recognition function has adjusted and the effect is gone.
— Thane Ruthenis, A Bear Case: My Predictions Regarding AI Progress