You're conflating the difficulty of migrating a complex system to anywhere with "vendor lock-in". It would be harder to migrate an Aurora RDS Postgresql instance to an Aurora RDS MySQL instance than it would be to migrate from Aurora RDS (postgres) to a hosted postgres anywhere else.
You're conflating the difficulty of migrating a complex system to anywhere with "vendor lock-in". It would be harder to migrate an Aurora RDS Postgresql instance to an Aurora RDS MySQL instance than it would be to migrate from Aurora RDS (postgres) to a hosted postgres anywhere else.
That to me screams "not vendor lock-in".