Thanks @power777 . We also have a similar solution where we loop through all products and construct the set of unique tags. We have had it for years and works well, but as we are getting larger and larger customers it is becoming less efficient and it would be nice to have a simple API call that would return all unique tags.
I had the same issue with ProductVendors and solved it the same way. Pulling all 30K products and getting their vendors, then recording the distinct list of vendors. I hit throttling 10-12X during this process because I am pulling all orders. It sure would be nice to be able to use the GraphiQL API as it was designed vs. having to draw down thousands of rows and sift through them.