I’ve been reworking an AddOn I started a while back before Classic and was for Retail that would detect premades. It works like Gatherer and GathererDB, and the main AddOn stores data for each Battleground that you can enter. I’m still working out the UI as I’m just using Blizzard’s UI, but it needs a little love. I have designed the UI in Figma; I just need to read up on creating the UI I’ve designed.
So far, I have about 29 people using it and taking the file acting as a DB that you can make a pull request to the repo on GitHub as the more data is collected, the more accurate it is at warning you about a premade. Currently, I have 464 EoTS’s played as it uses the calendar to show and collect data for weekend BGs (I plan to add an option to collect all, but I need to find a good way to index the DB file.)
If there is enough interest, I will spool up a server and quick CRA on Digital Ocean to upload the data files there, and I will update the plugin and or have the most up-to-date DB file for importing. It’s been a big eye-opener, and kind of baffled by Horde outnumbering Alliance premades 5:1. Yes, that much of a difference. In EoTS I just merged the latest PRs I had and found a ton of multi-5-mans in EoTS. When I say a ton, over half seem to be two different servers with 5-man premade.
Not sure if Alliance just isn’t queueing in premades, but I have roughly 50/50 data from each faction. I’ve taken green geared alts into Horde games and win in about 5 minutes with an average of 830ish honor, and Alliance is sometimes lucky to get 120ish honor, lol. I tried to get this on Curse, but it was removed a while back, so I’ll keep it on GitHub to read curse’s ToS and see what the issue could be. Nothing is being done that is against WoW’s ToS.
I’d like to get more Horde running the AddOn samples as I want to if I can put together a fact pattern where Horde is outnumbering Alliance in premades 5:1. If you know how to use GitHub and want to contribute or help collect data if enough interest I will link AddOn. Side-note, I’m also working on spinning up a UI on the Web that shows the data and premades, kind of like a wall of shame 
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