As for more lock in, how? If I use aurora postgres serverless I am 100% free to migrate to a regular postgres server, even on another provider.
Nobody is thinking there is no server, except maybe my grandmother.
Aurora does add bells and whistles on top of vanilla Postgres that you’d be hard-pressed to find from other DBaaS vendors.
Sure, you can pg_dump and pg_restore to another provider but you lose all the goodies that made you choose Aurora in the first place.
For clarity, I’m a long-time happy user of Aurora and spend $super_big_money on it. Worth every penny IMHO.
I'm honestly curious as to which features you find most compelling that can't be found in vanilla Postgres.
But that single DB is just a piece of the business puzzle. Networking, web applications, even backups. That's hard to migrate (And hard here means it will take massive effort and time)
Good teams have plans in case they need to migrate. But I think not all teams are prepared for such scenario.