The real counterargument here is that the DB systems that stored nested data mostly lose in competition with relational systems over time as it turns out they don't satisfy the large number of people who use data for things other than UIs - they aren't suitable for long term storage and don't separate concerns in a way that allows generalists like database engineers to optimise how data gets too and from a storage location into memory.
And, in practice a lot of these frontenders end up storing a JSON blob with either no nesting or just one level of nesting that looks a lot like a database schema built by someone being stubborn about not normalising data. In some sense that is fine, databases seem to be learning to just treat simple JSON blobs as normalised data but it is hard to make that as efficient as a guaranteed schema. Plus larger companies often end up having to hire a dedicated team of engineers to properly normalise data so other people can use it.
And, in practice a lot of these frontenders end up storing a JSON blob with either no nesting or just one level of nesting that looks a lot like a database schema built by someone being stubborn about not normalising data. In some sense that is fine, databases seem to be learning to just treat simple JSON blobs as normalised data but it is hard to make that as efficient as a guaranteed schema. Plus larger companies often end up having to hire a dedicated team of engineers to properly normalise data so other people can use it.