> Making optimizations based on telemetry from real world sites doesn't mean you're optimizing for that one site only, like a video driver including hacks for a specific game. For example, shifting an array in Firefox used to be O(n) vs. O(1) in the competition [1]. Improving these sort of code paths benefits the entire web, even if the performance issue is discovered and profiled on docs.google.com.

Again, the question should be if something "benefits the entire web", how can we discover it without an opt-out anti-feature? If the answer is we can't, then we don't want it. It is as simple as that.