Maybe I'm missing something but as the other comments have pointed out, this is very low scale. I'm not sure it can even be called at-scale in any sense these days. Also the architecture seems incredibly fragile and complicated for what it's doing. I get that they've built some integrations and backend processes to assemble this data but the API serving could all run on a single app and database server since it's all…
In hindsight I should have added more information about where the actual work is being done -- I definitely missed the mark on parts of this post.
The lions-share of our work is done in an async fashion. 2M API requests (lookups) turns into 40M+ background jobs. These jobs fetch, aggregate, and scrub data from a number of downstream providers.