So you have a ratio of 1:7 between YugabyteDB and PostgreSQL on single node. This is not surprising. Even when you run on single node, the database is optimized for distributed transactions. When you see the advantage of YugabyteDB is:
- when going to replication factor RF=3 because then you have no-data-loss-HA which you cannot have with PostgreSQL
- and adding nodes because the load can be balanced over multiple machines. And then the rates will linearly increase
Running on single node without HA protection is faster on PostgreSQL. But it cannot scale out.