You don't need multiple postmasters to spawn connection processes, if you have a set of Postgres proxies each maintaining a set pool of long-standing connections, and parceling them out to application servers upon request. When your proxies use up all their allocated connections, they throttle the application servers rather than overwhelming Postgres itself (either postmaster or query-serving systems).

That said, proxies aren't perfect. https://jpcamara.com/2023/04/12/pgbouncer-is-useful.html outlines some dangers of using them (particularly when you might need session-level variables). My understanding is that PgDog does more tracking that mitigates some of these issues, but some of these are fundamental to the model. They're not a drop-in component the way other "proxies" might be.