I agree with you. MySQL lost a ton of momentum because of Oracle but given what Oracle is doing with the original MySQL, I suspect keeping up with it does not require as much effort as it did getting to where it is now. If MySQL forks get the developer attention they need, and set themselves up in a way they can share code between themselves and, maybe, with PostgreSQL, it will continue evolving.
Having one single corporate sponsor is always a very bad idea for open-source projects. I hope MySQL derivatives have learned this lesson.
And, I imagine, the dual-licensing thing has to go. That's no longer a viable way to sustain development.
Percona Server exists because Percona has a great deal of deep hands on knowledge about MySQL tuning and internals, and has a live-or-die commitment to making MySQL work well, and taking patches from it's user community.
Maria and Percona server advance more or less together, and routinely swap patches back and forth.
DrizzleDB exists because some of the MySQL developers decided that Doing It Right was more important than maintaining old targets and maintaining backwards compatibility.
There is plenty of room in the MySQL user and developer ecology for both approaches. If you need MySQL, and you don't trust Oracle, or don't want to pay them, just swap in MariaDB or Percona Server, they are drop-in replacements. In fact, you should drop them in away, they have more bugs fixed and are more performant than stock Oracle MySQL.