By default elasticsearch stores data in 3 ways: rowstore (original doc/row), inverted-index (for fast queries), doc-values (columnar store for aggregations). So you need to configure it for what you want, for each field.

While you can do all of that with plain pg and having no indexes and doing table-scans, it will be slow when you search (depends on how often you need to search and type of queries).

So es is very good at some stuff compared to every other type of db. For logging, yeah, there are some companies who just do full-scan on each query and are fine.