I've created a big system with only SQL in the past like you just said. I wouldn't do it again because of these two pain points that I had to deal with: 1. it'

I've created a big system with only SQL in the past like you just said. I wouldn't do it again because of these two pain points that I had to deal with: 1. it's really hard to debug SQL queries and stored procedures (at least it was in Postgres 11) 2. when you hit a performance bottleneck, you don't have much control over it - parallelizing is hard and you have to trick the query planner to do what you want (and it doesn't work sometimes)