This seems like an excessively uncharitable read of the situation. I've never used Nubank's software, but I have used (on-prem) Datomic and I certainly wouldn't say it has bugs everywhere. In fact, in my (admittedly low-volume and simple) usage of the system I haven't come across any bugs I can remember. Calling Cognitect a "burnout" company is inaccurate and rude.

I agree with you that the Datomic cloud stuff comes across as being frighteningly complex. I think they probably just need to work on the documentation, like making it more obvious what the differences and tradeoffs are between the deployment scenarios.

Did you inherit a Datomic system that was previously developed by a small team or a small company? Because inheriting a system that's hard to understand and change transcends languages and databases. It is the tie that binds us all as software developers.