Yep, the reason ElasticSearch is fast here is that the underlying Lucene indexes essentially form a column-oriented database. This is superb for low-cardinality fields like "object->>environment"; if it has just a handful of values, then only those values are stored, as a sorted list of postings. Intersection with other field-based constraint are vector operations and can be super fast.

I suspect that to make a fast-counting time series mechanism for Postgres, you'd need to create a new index type that used a columnar approach (or even used Lucene unerneath). I don't know much about what optimization options are available to Postgres extensions, but it doesn't sound like it would be impossible.