Last time I checked, it was still hard to get a Google CloudSQL DB into BigQuery, so I’m surprised they did the sheets integration first. We used a third party that just copied data from our CloudSQL to BigQuery.
A job that should be less than an hour took over 6 hours due to various annoying datatype issues.
Another interesting thing is that BigQuery doesn't have Full Text Search so you need to go back into postgres or use elastisearch to use FTS which is beyond annoying.