These are valid push-backs on the "postgres everywhere" argument.
The two critical questions IMO are:
1. At what scale do these issues arise?
2. Does Postgres make it harder to solve them when you reach that scale than another solution would have?
Some of that probably depends on the libraries or tools you use on top of Postgres but being able to easily swap to Redis or a proper queue at scale should mitigate the risk of starting with Postgres if you don't already have the scale.
The two critical questions IMO are:
1. At what scale do these issues arise? 2. Does Postgres make it harder to solve them when you reach that scale than another solution would have?
Some of that probably depends on the libraries or tools you use on top of Postgres but being able to easily swap to Redis or a proper queue at scale should mitigate the risk of starting with Postgres if you don't already have the scale.