on the other hand, an internet company playing fast and loose with EU cookie opt-outs seems so par for the course that I would take it as more suspicious if they were not?
And I, like many, avoid business with any such companies who display a contempt for personal data.
If my ISP did such a thing, they would be very quickly reported to the Information Commissioner. Also, I think you will find the UK is beholden to the GDPR. It isn't simply an "EU cookie" law as you seam to imply.