Yeah sounds like they liked it because of the infinitely scalable storage and high write throughput, but don’t really get into if they were having issues with all that on MySQL. Also, they use the term “analytics” a lot, but it seems to be a different use case than typical OLAP workloads since they were serving this data to customers adhoc.
Scaling writes on MySQL/Postgres is a huge PITA once you hit the point where a single master on a chonky server can't handle it anymore and you lose most of the benefits of being on a relational db.