However, just a side note: Steemit Inc.'s API & infrastructure costs are in the millions of dollars per year. A "normal" API node costs max 1000€ per month, so roughly 12,000€ per year.

Few mis configured EBS volumes with crazy IOPS values, Cloudfront, heavy usage of Docker based builds etc can be the reason for the high costs. AWS is not the right solution for something like steemit.com which has no per-visitor or per-user revenue model or challenges with capacity.