A tweet doing the rounds says LinkedIn merged four job titles into one. The quote is real, the role is real, and the arithmetic everyone read into it is not — and the difference is the whole career signal.
Product metrics answer a different question from "is the frontend fast?" — they ask whether the product delivers value: do people show up, do they reach the aha moment, do they come back, and do they stick around. Almost all of it is measured in the browser by frontend event tracking, but the numbers describe the product, not the frontend's health. Here's the set that actually changes decisions.