It's a small team, and this was announced I think nearly a year ago. It's a pity that apparently the import isn't without issue, but I can see how they expect expert users to be able to fix any problems they encounter.
The whole multiple keychain-thing is or was not communicated clearly anywhere ever, I've stumbled on this before. That's part of the bad design though, a keychain file would have made so much more sense and be easier to reason about than configuring it through arcane gpg incantations. I steered clear of it, but I'm surprised that Enigmail supported it (did it?).
Anyway, one 'internal' ring is a very good idea, and I'm happy TB went that way. That was a very conscious decision, as Openpgp.js development is much more active and open, so don't count on this changing.
The new UI could use some polishing (one or zero click encryption please!) but generally I am happy, and happy that I don't need Enigmail anymore.
I initially tried to fix this by messing with my GPG keychain, because my underlying assumption was that they shared keychains. Imagine my shock when I realised my assumption was wrong! Fortunately I didn't lose anything important. Either way, having to maintain separate keychains is already enough of a deal-breaker for me... Maybe it will improve over time. I guess I'll have to wait and see, as I didn't back up my TB68 profile, so I can't downgrade :(