Let's take a hypothetical scenario of a random pug doing an Omega Savage floor. The fight has an enrage timer, so the party together has to reach a specific party DPS number to be able to clear it. Everyone else is pulling their weight, but there's 1 DD who is doing significantly less DPS than they should - and the whole party is failing because of that one person.
Now there are 3 possible scenarios that follow in this situation:
1) There is no official parser and talking about parses isn't allowed. The group has no way of knowing for certain why they keep wiping to enrage over and over and over (everyone is geared, seem to follow their rotation, and have beaten the dummy for the fight, no one is dying). The party ends up disbanding, confused and frustrated, all wondering if it was them or someone else who was holding the group back (because they're all PS4 players and can't know what was the reason for their failure).
2) There is an official parser, so the group can see right away who can't meet the enrage requirements. The party will politely inform the person that they're unfortunately preventing the group from winning and need some more practice with their rotation before joining a kill party. Or, better yet, the person will notice this themself and leave the party to get some more practice. The underperforming DD is replaced and the party will get their win.
3) There is an official parser, so the group can see right away who can't meet the enrage requirements. The party will immediately start belittling and harassing the player at fault, removing them from the party and calling them all kinds of awful names. This is considered harassment, and the party members doing it will get reported and punished.
Without official parser, only option 1 is possible (in theory, since in reality pretty much all groups already have at least 1 person parsing). With an official parser, both options 2 and 3 are possible, but option 3 is still not allowed in game.
As long as there are fights with an enrage timer, and each party member has to push certain amount of DPS so that the party can win a fight, parsers are needed. And, more specifically, group parsers are needed, to prevent scenario 1. This is why there should be an option to have an official group parser available for content such as extreme primals and Savage. It could be enabled or disabled with party finder, and players could choose if they wish to join a group that has one or a group that doesn't. This would not hurt anyone in any way (apart from players who would like to sneak in these parties without being able to contribute enough for the party to clear the fight).