The Relational databaes like Mysql, MS Sql are not the only ne available these days there are many more variants available at the moment. But the blockchain storage and its query engine has not evolved that much its still very much outdated and there is need to update that which no project has done till date.
Yes from 2015 onward Dremel/MPP has taken over like Impala, Presto, Drill. I hardly see any blockchain project that is using these technologies. There is need to use these technologies to expedite the process SQL query. Right now storage is the biggest issue in blockchain projects.