It doesn't exactly need to be Chrome-specific; every browser/JS engine will have slightly different performance on different workloads, so Google just has to lean heavily on things that are golden-path for Chrome. They could even do this accidentally/nonmaliciously just by mostly testing on Chrome and not testing performance on other browsers.
Wouldn't it rather be "Maintaining and not fixing" rather than "Designing"?
Google is perfectly allowed to make mistakes or forget something. The criticism is that this is a repeated behavior, as if they decided that it is never going to be a priority.
