I've always found doing logic and processing in the database to be much faster and much more efficient than doing it outside. The closer you can process data to the data store, the faster it goes. Using materialized views can get you a long ways.
It goes much faster I agree. However you are very short sighted. That black box doesn't go on forever. It will work fine for the first 50 users, seems ok for the next 100, 500 we're doing ok. 1000 BOOM! Then what do you do?
I'd rather have a slightly higher latency and be able to scale to 100,000 users.
Materialized views are not needed with CQRS architecture. ALL tables (or sets) are materialized views already. No joins are ever made.
dblink is ugly and if you ask me a problem, not a solution (latency, network io, memory).
I'm not sure what you classify as "larger" but I'm talking tens of Tb, 1500 tables and over 2 million LOC in the application.