This is akin to saying "we replaced the tires on the car and the average user didn't notice". If the entire car was replaced, then maybe we get a bit more excited.

However if "replacing small sections of code" is heralded as "the most amazing achievement in software development" then we've all lost the plot a little bit somewhere.

It makes sense both ways, no?

The reality is, of course, most people aren't going to notice. If the functionality and performance is 1:1 why would they? Is it impressive? A bit, but not how you're positioning it. People seem to forget LLMs are good at what they've learned from training data. And the LLM is good at compressing time. The only notable thing about these types of marketing spins is that a rewrite was accomplished in a small time frame that was hard to pull off before LLMs. The actual act of the move is less so.

Did the codebase improve? Is it more performant? I've seen nothing to really stake those claims with any objectiveness. Lastly: what was gained?