It really isn't as black and white as that. I completely understand why SE don't want parsers in the game because I have seen what happens when a game allows it.
Many people misuse parsers. They glance at numbers without taking things like gear or someone else making that person's job harder into consideration. They look at a tiny portion of the picture and judge someone as if that's the whole story.
Sure you can inform them that they're not looking at the big picture but this can be met with resistance. So then an argument starts when all you wanted to do was tell someone that taking a glance at a parser is often not enough to know what is truly going on.
And it really sucks when the person getting criticised also doesn't know how to look at parser data correctly and actually believe they are bad at the game when they're told they are. Some players are not experienced enough to realise how much someone else's performance can impact their own.
Also there are players who expect perfection all the time from those around them and nitpick tiny mistakes or have a hissy fit because someone in normal mode doesn't have excellent ogcd use when it's not even required in normal mode. Some people are just incapable of adjusting their expectations for the content they're in.
The problem isn't the parsers, it's the people who misuse them.
I'm not against parsers, if I was I wouldn't touch savage with a ten foot pole. I'm against their misuse but because misuse is not something that is possible to fix SE have elected to not permit them. In their eyes in game parsers are more trouble than they're worth.
That said it would be nice if there was a personal parser in the game that gave you data and a grade that takes your ilvl into account after you exit the instance so you can examine it yourself at your own pace without the risk of someone ignorant or meanspirited giving you an unnecessarily hard time over your performance while in the middle of doing it. SE are really good at making nice and clean UIs that are easy to understand so I'm sure any parser they would create would be quite user friendly. But even if that was in the game some people would hound someone after they exit the instance to call them out on something and that can lead to drama as well...so I doubt we will ever get anything like this.
Until the community can prove that parser misuse and the toxicity that can come from that would be rare SE are never going to give us a parser.