> Thing is, the proof EY got from Wirecard was good enough to meet these thresholds

It objectively wasn't. I've never heard of a case where the auditor doesn't independently verify the bank account balance with the bank itself. More reliable evidence reduces the need for additional corroborating evidence. In general the evidence obtained from the company itself wouldn't be considered reliable by itself.

https://www.ft.com/content/db9fa3d7-11da-476e-beea-d5ed0ad13...

This wasn't some hard to uncover marvel of accounting fraud using complex financial engineering.