Oh, and pointy jab: these folks are also, in my opinion/experience, the most eager to vibecode shit. Make of that what you will.
Swore blind it couldn't be improved.
By next morning's stand-up, I'd found it was doing something pointless, confirmed with the CTO that the thing it was doing was genuinely pointless and I'd not missed anything surprising, removed the pointless thing, and gotten the 10 minutes down to 200 milliseconds.
I'm not sure if you're right or wrong about the correlation with vibe-coding here, but I will say that co-workers's code was significantly worse than Claude on the one hand, and that on the other I have managed to convince Codex to recompute an Isochrone map of Berlin at 13 fps in a web browser.
But I know stories like yours from a decade past as well. A tale old as time, but compounding in recent years - IMHO.