[fuy]

I love and use Postgres daily for many years, but:

Performance monitoring is pretty much absent, all you have is pg_stat_statements and friends. So for any serious scale you need 3d party solution (or you're writing your own) straight away.

HA is complicated. Patroni is the best option now, but it's quite far from experience SQL Server or Oracle provide.

Optimizer is still quite a bit simpler than in SQL server/Oracle. One big thing that is missing for me is "adaptive" query processing (there's AQP extension, but it's not a part of distribution). Even basic adaptive features help a lot when optimizer is doing stupid things (I'm not gonna bring up query hints here :))