No, the point isn’t to develop on the beta, it’s to know up-front, early on, specifically what’s breaking because of the new OS. Check back periodically as they update it. If the same poopies is broken after a few builds and you haven’t at least taken note of the issues down and maybe brainstormed some very general, off-the-cuff potential fixes, then when they wind up still being issues in the GM you’ve got a huge head start.
It’s not like Steinberg could just NOT support the new OS eventually - they’re going to update it, end of story. They clearly decided that it was not a priority in this case to prepare for potential issues that’d be introduced with a new OS, and like you said: “Apple has been known” to do this. Steinberg can’t claim ignorance here - I’m not saying they just sat on their asses doing nothing (although we’re still not good on Retina machines and don’t get very frequent updates…), but they pretty plainly didn’t prioritize for this but are trying to pass it on as if it’s Apples fault.