Michael, you are right. There is no such filtering available.
I don't understand why such option is missing. Salesforce is a popular and critical database. The connector from Tableau is half baked.
Maybe we just hit the limit of Tableau as an extractor, which Tableau is not supposed to be.
Our workaround is to use Alteryx to do the extraction into a tde file. Since the data volume is huge and Salesforce times out often, I even have to create an incremental extractor for it. It decreased the daily extraction time from hours to minutes.
Another workaround could be creating a custom table within Salesforce with the minimum data you need, so that you can reduce the amount of data to extract. I didn't try this. Just a thought.