We already know people already made their own parsers so you could just use one of those, that measure damage done, dps and many other things.

Problem is without one in game people everyone can't measure their performance since its not available to everyone, only to people who got their own parser program. If I see 2 monks one has all the base af3 pieces while the other has all the +2. The one with the +2 gear will outperform the one with the base gear but then there is no way to tell, the difference between the two. You can eyeball the chat log but that just isn't good enough.

There are a bunch of small things you can do to improve dps without a parser there is no way to tell or test what works better and what doesn't.

It would be more convenient to have one in the game, that you can link the logs to party chat so everyone can see.