I think you and pretty much every other person that states this is missing the point here.
First off, existing parser results are also tainted and skewed by the rest of the group, does that make that useless too?
Secondly, you show me a player that manages 5-5.4k in a raid boss encounter and I'll show you a player that's either practiced extensively with a parser or is using proven rotations and openers that were also built upon data from a parser.
Other than top end PS4 players, this isn't for that crowd. They already have better.
This is about taking a tool, simplifying and removing the fear/hassle/platform factor from it and as such, making it accessible to the masses that might well want it.
This is for the people that might only be doing 1.5k-2k DPS (Or perhaps even less). They might well overhear friends in an FC or LS discussing what damage they did in their 24 man or they might even see figures banded about on here or Reddit. This is the part where they realise that hey, they are likely doing something quite significantly wrong. It's about getting that first spark in the hope that it'll ignite a desire to up their game and play at a more respectable standard.
Even if it gets 1 in 4 of those sub 2K DPS doing 3K+, that's a huge win in casual end game content.
TLDR: Those that are optimising the last 10% of their role are likely already using something better, this isn't meant to replace or supersede that. This is a taster for the masses.
Yes it would almost certainly be inferior, but it absolutely will not be useless (Unless SE chose to cripple it to that stage of course). This is 2018, try seeing in colour rather than black and white. You might like it.