I think a big point of the article was that these more recent relational dbs (like memsql) figured out how to make distributed joins across multiple shards scale really well - that's one of their core value adds. So you can shard your for example customer and order data stored across multiple nodes and partitions and do distributed joins, aggregations etc. Scaling to use hardware resources on multiple machines is a crucial aspect of these systems.

Disclaimer, I work at Memsql, speaking for myself.