Postgres doesn't even hold a candle to the OLTP performance that Oracle is capable of. It is probably decades ahead of Postgres in terms of technology. Oracle had multi-instance capability 22 years ago. Robust multi-instance support still seems to elude Postgres. Postgres high availability and failover capabilities are laughable.
Sure, Postgres is much easier to setup and tune (because it does much less compared to Oracle anyway), but it's not going to dethrone Oracle anytime soon when it comes to powering the most demanding OLTP workloads (like stock exchanges and telecom) out there.