Outbrain uses ScyllaDB in production at scale across multiple data centers. Not sure if it's Instagram scale, but still enough to prove it's reliability and performance.
Data density is a thing. If u putting 10tb on a c* host, switching to Scylla doesn’t fix the issues that putting 1pb of data on a host would involve (ie backing that up). Throughput of 100mb of data done in marketing benchmarks are rarely relevant.
Ok, but that's a different issue and nobody is suggesting 1PB of data on a single node as a good idea. The comment was that "scale" is more than just a simple count of nodes. Even if you keep the data the same size, Scylla can handle it with much better performance which is a good enough reason for many to use it.