Postgres LISTEN/NOTIFY does not scale

RBDMS are not designed for write-heavy applications, they are designed for read-heavy analysis. Also, an RDBMS is not a message queue or an RPC transport.

I feel like somebody needs to write a book on system architecture for Gen Z that's just filled with memes. A funny cat pic telling people not to use the wrong tool will probably make more of an impact than an old fogey in a comment section wagging his finger.

People have been using RDBMS' for write-heavy workflows for forever. Some people even use stored procs or triggers for getting complicated write operations to work properly.

Databases can do a lot of stuff, and if you're not hurting for DB performance it can be a good idea to just... do it in the database. The advantage is that, if the DB does it, you're much less likely to break things. Putting data constraints in application code can be done, but then you're just waiting for the day those constraints are broken.