You can already do this in fact players do this all the time.
"---- Ex No 100 Law bonus"
"A-s No first timers, know up to ---- phase"
I'm not sure how saying "---- Ex, be able to do 1500 DPS" is any different.
Even if that were the case and say 5-10 of these types of parties started showing up in the PF, would you mind telling me what exactly is stopping you from creating a party that doesn't set that as a requirement?
The problem with the harassment and segregation arguments is that those making them conveniently forget that it already happens and try to attribute the behavior to parsing.
We have no issue currently with calling out and kicking tanks / healers who aren't performing up to par but the second DPS accountability is brought up it's suddenly a huge community concern. We already have tons of PFs that have various leader set requirements ranging from "No first timers" to "X item on lock" and have had so since the launch of the game but someone brings up parsers and now it's a segregation issue?
Players won't be able to understand parsers? is that really an argument?
10 seconds worth of tooltips and a tutorial could easily solve that, they could even go the extra mile and add a guildhest explaining it, it's like people are jumping through every hoop imaginable to try to find new and inventive ways to prevent DPS players from trying to improve or be held accountable for their role, and i say DPS because once again we have zero issues as a community calling out and kicking tanks and healers currently and not only can nobody accurately explain why this is, they instead sit here and sheepishly avoid the issue because they know it throws a wrench into the whole counter argument.
"It will give players a tool to harasss others"
"The community will become toxic"
These keep getting tossed around as justification as if parsers haven't been a part of MMO culture for over a decade, when time and time again the largest player response if any is apathy. This isn't uncharted territory nor are any of the results hypotheticals, we already know what will happen and we've seen it many times before. Would it promote toxicity in this game? maybe for the first few weeks to a month as the community adjusts like they do any large shift in gameplay changes, like the WAR rework or the Wanderer's minuet addition to BRD but after time they'll recover, get over it and get used to it.
Private parsers? Hide your DPS?
Why would SE go through the trouble of creating an in-game addition that is inferior to a third party alternative? If anything that option would be more "toxic" because you'd have arguments about players trying to hide from criticism once the wipes hit.
Players who are likely to harass others over DPS are just as likely to harass them for other reasons, and some of them already do. However this is what the GM staff is for to report these issues so that they can be dealt with accordingly.
I don't say this to offend anyone, but please realize that many of the points that are being made as a counter argument against this have been dis-proven like... 9 years ago.