I understand betas very well, but something as critical as that seems more fitting for an alpha. Liquid glass notifications on top of a bright wallpaper, bleeding together so you couldn't read or see anything shouldn't be in a beta.
Obviously Apple can improve things for the final release (and it seems like they're taking some steps in that direction). But these issues should have been identified long before the beta was released, and the fact that they weren't does not inspire confidence.
At the same time, there seems to be precious little time between when Apple decides a feature is going to ship in the next release, and when WWDC happens.
Even if there was common knowledge inside the company that a new UI was coming, it may have not been merged into mainline until closer to WWDC. At that point, individual teams will need to alter their code to build and be usable on top of the UI as part of continuing their own development - but were likely still focused on the death march for their own WWDC-launched features.