People are misunderstanding the custom bluetooth chip. It's not for phone-to-airpod. It's for airpod-to-airpod. I believe this is how other similar products work. They rely on bluetooth for the phone connection, but then another wireless technology to connect each earbud.
Good observation. But that doesn't preclude the same chip being updated overall to connect to the phone. Apple sits on the BT SIG, so they developed BT 5. I've been saying ever since that article came out that Apple is in a position to implement BT 5 products ahead of everyone else, since they know the specs, and that they would likely create their own chips rather than waiting for anyone else to implement the new specs that got released too late to make it into the iPhone. So what we'll see is a BT 5 chip with a custom "draft" protocol which Apple will likely try to steer into the BT 6 specs with their position on the board, just like Apple has been an instrumental partner in USB & USB-C. There's absolutely no need to go proprietary here if they want to push the wireless standard, just like they pushed USB originally.