Ugh. Pain. I'm hiring, and I've been filtering out resumes that are heavy on these kinds of metrics.
Because I literally get thousands of entries with these kinds of wording. Often with excessively precise numbers, like "by 23.5%".
My problem is that it's hard to tell the amount of real work it took to do that. It might have been as stupid as creating an additional index in the database, or it might have involved a deep refactoring across multiple systems with a zero-downtime gradual rollout.
I would prefer something like: "I worked as the hands-on leading developer to do a large-scale refactor on the highly loaded front-end network routing system, resulting in user-visible latency decrease on the Youtube front page".
For me the key words are: "hands-on" (and not just writing a product brief and getting resources for it), "large-scale refactor" (so likely not just creating an additional database index), "highly loaded".