You're incorrect, or at least that's what this complaint claims, and I personally have been expecting it for awhile.
The fact that cookies are pseudonymous has 0 effect here -- literally their entire purpose is to be able to associate third party data with a person's browser.
Your contention that all they're used for is frequency capping isn't true either, but even if it was, it's not relevant -- "I'm just using it for frequency capping" isn't acceptable under the GDPR, just as much as "I need the data to do advertising" isn't a reason acceptable under the GDPR for keeping a piece of data in the first place.
Here's the text of the GDPR on cookies: https://gdpr-info.eu/recitals/no-30/