Those aren't problems of Bluetooth, those are problems of device implementations. The BT protocol makes it possible to manage pairings, un-pairings, and re-pairings, in any which way that makes good sense for the user. But a lot of device manufacturers don't spend the time to read even the most basic parts of the spec necessary to manage connections.
For example, a lot of re-pairing issues come about from the device resetting its own device ID. Some rare devices do this on every soft-power-cycle. A good many devices do it on recovering from power-failure (e.g. dead battery). At that point, the device is basically a completely different "device". The best devices keep their device ID in non-volatile memory so they can recover from power failure without resetting their device ID.
Having built a few BT devices as a hobbyist, it's not really that hard to make a good pairing experience. You just have to... think things through and not do the most bare minimum work.
I have many BT devices, from budget to high-end, and they all have problems, from minor to major.
I stress "from minor to major"; in my experience BT does ultimately work, but there are always minor, odd, kinks like (I assume) an Android update preventing my headhphones to establish a "media" connection 50%+ of the time.
Given that also my high-end devices are subject to problems (eg. ~400$ mobile phone with ~400$ headphones), then the specification may be technically correct but practically unusable.
Having implemented a few devices, honestly, the spec couldn't be more straight forward. It's really a case of hardware engineers being terrible at user experience. Just because a device is expensive doesn't mean the company has put all necessary effort into the BT stack. Look at how many "simple" things Apple, Google, and Facebook screw up on a daily basis.
Yes, when it comes to protocols a lot of companies seem to have an attitude of "when it works, don't touch it", and the result is a mediocre experience because they forget to look at the edge cases.
For example, a lot of re-pairing issues come about from the device resetting its own device ID. Some rare devices do this on every soft-power-cycle. A good many devices do it on recovering from power-failure (e.g. dead battery). At that point, the device is basically a completely different "device". The best devices keep their device ID in non-volatile memory so they can recover from power failure without resetting their device ID.
Having built a few BT devices as a hobbyist, it's not really that hard to make a good pairing experience. You just have to... think things through and not do the most bare minimum work.