While yes, tight-knit savage teams may not lie to each other or care, the problem with this arises from often times when a member of a static is missing you have to PUG from the general population or, alternatively, try the fights with a complete PF made party (especially happens in Extreme primals). You may get someone who knows what they're doing or you may get someone who is completely new and just wants to give it a try. One of the long time points of the pro-parser crowd is that if you build a PUG party that can't clear a DPS check, you don't have any official way of knowing who isn't pulling their weight. While I'm all for being inclusive, if someone is not capable enough at their job to meet an average DPS necessity of high-end content then they don't really have a place there until they can improve to a point of meeting said check.
Now the typical counter-argument for this is "well what's average or what is the standard" but I feel that argument is assuming that people doing high end raids have never seen other people play or never pay attention to what others are getting. If a parser was available for high end content and I join a PUG and see a MCH doing 2000 DPS, I'm not automatically going to assume that 2000 DPS is the standard for MCH in that fight. If my next party the MCH is doing 800 DPS, I will reasonably assume that one of them was incredibly skilled and doing very high DPS and the other is doing very low DPS with the average right around 1300. After 5 or 10 runs in which I have a MCH in my group, I will have a general idea of how much a MCH is able to do and be able to judge accordingly if someone isn't quite up to snuff from there on out. This would only be further aided by everyone having the parsing data and therefore being to ask your FC members or LSes what their average MCH has historically gotten if you feel the one in your group is not contributing to a DPS check.
Again I'm not advocating that person be disbarred from the fight forever; however, it's usually pretty clear that the party isn't going to pass a DPS check with a person who is consistently far below average. This would be a good time to remove said person which admittedly may be an ugly affair but the removed person would have empirical evidence that they need to practice their rotation and, whether it was stated nicely or meanly, they would at least walk out with knowledge of what their class should be doing DPS wise. Then they could turn to training dummies which would also be able to tell them their DPS and work on rotations until they are doing better and can try joining a group again. The glory of this is that once you have this information and know your rotation, you'll learn your proper rotation and shouldn't ever be kicked from a party again.... unless you can't get mechanics but that's far outside the parser debate.