How would an optional, official parser be toxic?

[HyoMinPark]

When I play my BRD, or another dps, I'm always looking at ways to make my damage go up. I examine my skills and try to come up with new rotations that will increase my dps. I don't need a parser to know if my damage is going up or not, since I know for a fact that it is due to the efficiency increase. I also don't need one to see if another player is performing poorly. Play the game enough and it's pretty clear most of the time.

Question though: how do you know you're being any more or less efficient by simply "coming up with new rotations", or that you're increasing your DPS by "coming up with new rotations", without quantifiable proof that such is the case? Feelycrafts aren't quantifiable, so you can't definitively say "this is better/worse than that" with no hard evidence of it.

Increasing personal efficiency takes more than just moving your rotation around. Especially on a job like BRD. Coming from a BRD main that optimizes the job.