It is not a decoration. Karpathy juxtaposes ChatGPT (which feels like a "better google" to most people) to Claude Code, which, apparently, feels different to him. It's a comparison between the two.
You might find this statement non-informative, but without two parts there's no comparison. That's really the semantics of the statement which Karpathy is trying to express.
ChatGPT-ish "it's not just" is annoying because the first part is usually a strawman, something reader considers trite. But it's not the case here.
Indeed, I was probably grumpy at the time I wrote the comment. I do find some truth in it still.
You're right ! The strawman theory is based.
But I think there's more to it, I find dislikable the structure of these sentences (which I find a bit sensationnalist for nothing, I don't know, maybe I am still grumpy).
Well, language is a subject to 'fashion' one-upmanship game: people want to demonstrate their sophistication, often by copying some "cool" patterns, but then over-used patterns become "uncool" cliche.
So it might be just a natural reaction to over-use of a particular pattern. This kind of stuff have been driving language evolution for millennia. Besides that, pompous style is often used in 'copy' (slogans and ads) which is something most people don't like.