The vast majority of the bugs reported by beta testers were fixed by the time the launch date rolled up. You just got unlucky where no beta testers had the same hardware configuration as you to test and discover bugs on.
That's the entire reason why the beta program is public, to get as many people as possible with a wide range of different hardware configurations to report as many bugs as possible in the early stages so they can fix them before launch.
There's a huge difference in something used by 100s or 1000s of people. Once something is used significantly more it'll result in bugs that nobody ever noticed before.
Further, the best way to keep things stable is regular timed releases. You seem to be advocating for releasing irregularly. Projects used to do that in the past. Regular releases result in way more stable software.