How would an optional, official parser be toxic?

[Penthea]

I'll see if I can find it for you, but I very firmly remember WoW Devs citing that their data has shown players have gotten better over the years. They attributed it to addons and community theorycrafting. Which includes parsers.

I would take that with a grain of salt considering there are add-ons that are designed to help you with your rotation. One called something like Spell Flash lit up the abilities you should be pressing. And no it isn't like FFXIV's combo system. It lit up absolutely everything in the rotation including major cds. Of course it is no replacement for personal class knowledge but the point is those add-ons are a crutch that can make players appear far more skilled than they actually are.

There are also add-ons that have trivialised some boss mechanics. For example Shadow Lord Iskar has a mechanic in which you had to pass around an object called "The Eye of Anzu" which required a great deal of coordination and situational awareness...unless you had the Shadow Lord Iskar Assist add-on which made the fight tremendously easier to do. Again, an add-on making players appear better than they actually are.