If database is shared it is a part of an API. If it is shared between teams then it is a public API.
If DB is shared then data from different users is entered/updated through multiple transactions. So you cannot get anything better regarding consistency and integrity compared to multiple DBs and distributed TXs.
By introducing schema change coordination you will introduce enormous delays to almost any DB change. This is more realistic than everyone knowing each use case but less practical. Shared DB is an antipattern either way.
If DB is shared then data from different users is entered/updated through multiple transactions. So you cannot get anything better regarding consistency and integrity compared to multiple DBs and distributed TXs.
By introducing schema change coordination you will introduce enormous delays to almost any DB change. This is more realistic than everyone knowing each use case but less practical. Shared DB is an antipattern either way.