> The index is 214 MB! That's almost half the size of the entire table. So the analysts are happy, but you? Not so much...

This is part of a broader choice: write amplification. You'd want to, of course, have the most precise index possible - but no matter how you cut it, you are incurring extra I/O for writes - one for the tuple, one per index. How you index things is heavily influenced by the mix of reads and writes, and this is why we have data warehouses/read replicas in the first place: it allows us to avoid write amplification in the write path, while having fast filtered reads (that are slightly delayed).

If you're dealing with <ridiculous number of users>, there is a good chance that you don't want to be putting BI/OLAP indices on your OLTP database. You probably don't have enough users to worry about this - but - if you ever find that your writes are becoming an issue this is something to consider.