I'm one of the makers of ParadeDB, a modern alternative to Elasticsearch. We build Postgres extensions to do fast search (pg_bm25) and analytics (pg_analytics). I love Postgres. If you have a small workload, like a startup, it certainly makes sense to stay within Postgres as long as you can.

The problem is, at scale, Postgres isn't the answer to everything. Each of the workloads one can put in Postgres start to grow into very specific requirements, you need to isolate systems to get independent scaling and resilience, etc. At this point, you need a stack of specialized solutions for each requirement, and that's where Postgres starts to no longer be enough.

There is a movement to build a Postgres version of most components on the stack (we are a part of it), and that might be a world where you can use Postgres at scale for everything. But really, each solution becomes quite a bit more than Postgres, and I doubt there will be a Postgres-based solution for every component of the stack.