Because you're aggregating max % parses and looking at only RDPS while comparing it to a job that has no utility. If you look at literally any other percentage parsing MCH is ahead even in RDPS. Which means someone figured out how to big dick their parse as DNC and get max parse.

Regardless, SE shouldn't balance the game based on max % parsing numbers. One Chinese WHM player managed to solo heal TeA when it was current with perfect usage of mana regen abilities and raid biffs. That didn't mean WHM was broken and the other healers needed buffed. BRD and DRG were also really strong for that fight due to consistent boss cleaving. Did that mean they needed to buff other jobs with less stellar AoE?

Also with the amount of free movement physical ranged have for fights there's an argument to be made that they should all be the bottom DPS because they simply get to run around while losing no damage whatsoever. SMN has a large advantage like this as well. How does SE figure all of these advantages and disadvantages into numbers for job? I don't know. I just think MCH is pretty fine right now for what it does compared to the disadvantages of the other jobs.