I assume you looked at the various Postgres functions, like width_bucket()?
I’ve never ran a PG-based TSDB so I’m reluctant to pass judgment one way or the other, but as I hope you can understand, “we have hundreds of columns in a table” is alarming at first glance.
The schema is organized by how we need to query it which is mostly by fetching all measurements for an entire day or month. Querying statistics on those metrics is not often needed, maybe a few times per week or day, so we do that in Snowflake if necessary. Or create a specialized streaming data flow when it the stats are queried more often.