I'm not bashing what they do on their time off lol.

But if they are off work, you literally are? Unless you asked for their holiday calendars, I'm not sure how you knew they were meant to be in work, rather than having the day off

The point is that the day before a large update the QA testers should be present with the team making changes.

Not many changes will happen the day before an update lol. Things like this will likely be cleared and agreed upon way before that. They thought (wrongly) that it was a safe update. Almost nothing should be actively being tested the day before release, because if the testers find something wrong, there is no time to develop a fix and re-test the fix.

But if you consider this small, and they still managed to fuck up this hard, what does that say about the QA team?

Nothing. It's a set of small changes. They didn't know there would be issues that could fuck this up hard, or else they would have tested it more thoroughly. It's the same thing as the ardy knight pouch change, would changing 50 coins to a sack of 50 coins mean 2.1b cash generated randomly? It shouldn't do, but even the tiniest of changes in programming can have massive effects.