[democracy]

fwiw we operate on layers and layers of someone else's code, that's not possible to understand how each dependency works, what's its performance, etc. And also do it for each new update of such libraries. Unless you develop in some very closed environment maybe, but for a modern java/js project that's not possible.

The reasonable approach is to load test the mostly used workflows, optimise if necessary - anything else would be fixing imaginary issues, working on non-existing problems, etc - there is normally no time or money for it.