As someone that's a senior at a large corp, I absolutely do not want someone making the codebase more complex with the only benefit being being that it's now barely measurably faster. Especially when there are probably better things to be spending time on (spoiler, there are). Unless you're knocking like 20% off a very impactful metric, or addressing a looming scaling probably, go find something better to do than making tiny algorithm optimizations.

I've seen rewrites at startups that were slower and less stable than what we had before and everyone cheered it on like clapping seals. This stuff is rife no matter the size of the company.

At least at large orgs there's hopefully someone able to measure it. The smaller you go it's silos all the way down.

Agreed. Hardware is almost always cheaper than engineering time, until it isn't, and that's when you should spend the time on targeted optimizations.