> I'm a bit of a control freak, so this lack of insight into the innards makes me (quite possibly unreasonable) uncomfortable
Ok, that could be the reason why you don't like Rails :)
Regarding postgres, its innards become relevant when you have partitioned tables with billions of rows and need to run queries on them for analytics purposes. In these cases you often need to manually create some complex queries from scratch; other times, you can use ActiveRecord "magic" up to a point, but then you either need to add special indexes (eg partial indexes, that saved my ass many times), or you need to replace the automatically-generated queries that ActiveRecord uses and which are good for small numbers, but become a bottleneck when scaling.
Ok, that could be the reason why you don't like Rails :)
Regarding postgres, its innards become relevant when you have partitioned tables with billions of rows and need to run queries on them for analytics purposes. In these cases you often need to manually create some complex queries from scratch; other times, you can use ActiveRecord "magic" up to a point, but then you either need to add special indexes (eg partial indexes, that saved my ass many times), or you need to replace the automatically-generated queries that ActiveRecord uses and which are good for small numbers, but become a bottleneck when scaling.