/sit enrage still works according to a streamer

First off, stop spreading misinformation and outright lies about things you clearly have no clue about.

Secondly…

Mashing X to gain charges was in vanilla and it was due to spell batching:

These videos were NOT from private servers but from retail Vanilla:

Published on Aug 8, 2006

originally published on warcraft movies on 2006-02-24 https://www.warcraftmovies.com/movieview.php?id=15930

and this was taken from the CLASSIC BETA a few days ago…

TLDR - /sit is NOT the same as mashing your X button to both sit and then stand:

Baconn
<Reverends of Swagger>
120
Human Paladin22915
Normally if you’re sitting down you would not get Reckoning charges from auto-attacks. However, you could gain charges from random NPCs by constantly sitting and standing up due to server lag: mob would try to attack you as your were sitting, so it’d be a forced crit. However, if you stood up just as you were getting hit, the server would see you as if you were standing and get a Reckoning charge.

^^^that’s from Baconn^^^
the Paladin who wrote the blue stickied Reckoning guide on the original vanilla wow forums:

Poster: Baconn at 5/25/2006 11:30:17 AM PDT
Subject: Guide to Reckoning V2 (Current 1.10)
http://blue.cardplace.com/cache/wow-paladin/1069149.htm

The Blue post was written by a Vanilla PLAYER - not a Blizzard Dev or CM - all the CM did was sticky it. After patch 1.10, Baconn (the author of the stickied post) never bothered to update it.