It does seem like a glaring omission, especially at the modest database sizes they used. Even something like PG with the Citus extension to compare parallelism

It does seem like a glaring omission, especially at the modest database sizes they used. Even something like PG with the Citus extension to compare parallelism would have been relevant. EDIT: Although another comment suggests that the data for the paper could have been gathered as long ago as 2016, which could mean Citus was not yet open source.