The devs design content initially according to their vision and demographic of whom that content is intended for.
They set a baseline for mechanics, dps checks and time vs reward ratios (used to be risk v reward but they moved on to time to complete these days)
They also datamine constantly on what players are doing and how (or how fast) they're doing it. When they see a significant group of players blowing through their baseline dps checks, the devs will investigate and adjust content accordingly...maybe for current content but most definitely for future content.
Now if the only reason people are blowing through those dps checks is because they're using unauthorized 3rd party tools wouldn't matter when it comes to adjusting content. People are doing things beyond what the devs initially designed for and they have to account for that no matter what...parser use or not.
It's not just dps checks. Devs in any game do this if they see players are power leveling through a certain method, they might nerf that method. If they're bum-rushing a dungeon then locking out the mobs out of the boss room to avoid clearing trash, they might, i don't know, put mob gates to prevent progressing till you kill those mobs.
Devs will always adjust content based on what players are doing. This is an mmo but people seem to think what they do have no effect on everyone else, but certain things do when the devs nerf or bumps up difficulty according to what some players are doing.
Ofcourse, that usually means people who are playing the game as intended might get screwed...or have to wait for echoed content.
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To people getting harrassed by parser users, the only thing you can do is report them for harrassment, copy/paste the chat text or link to where they posted pics on their parser use. If SE doesn't care, then you're no worse for wear. Otherwise they will deal with it.