There definitely have been people who have implemented a more pure relational model (e.g. https://docs.relational.ai/rel https://docs.relational.ai/rel) -- and

There definitely have been people who have implemented a more pure relational model (e.g. https://docs.relational.ai/rel https://docs.relational.ai/rel) -- and at scale, too. There's just so much force and legacy behind SQL that it is pretty much impossible to do well in the industry without it. But the relational model works and has been proven, independent of SQL. Hell, even Datomic.