That really isn't his gripe. In fact near the end he describes would have been a good direction for starting fresh.
His pain is that it's been 17 years and some basic core functionality is either still broken or entirely missing. It's not my expertise so I don't know if it could have been planned any better, but 17 years and _basics_ still being broken doesn't sound great.
I think part of the issue is that there's a couple of misconception about Wayland. Wayland focuses, exclusively, on being a window management protocol. Use cases such as screen sharing and accessibility are out of scope for such. Instead, they were supposed to be implemented through their own protocols. But those protocols didn't show up for a long while.
His pain is that it's been 17 years and some basic core functionality is either still broken or entirely missing. It's not my expertise so I don't know if it could have been planned any better, but 17 years and _basics_ still being broken doesn't sound great.