DSE reports the Cassandra version it is based on in system.local.release_version. When the OSS driver connects to DSE, it uses that to decide how to parse the schema (it doesn't know that it's connecting to DSE).
Sadly, modern DSE versions report a misleading C* version: 126.96.36.199xx, which is "close" to 4.0.0, but definitely not "higher" (4.0.0 is not even GA yet).
In particular, DSE 6.0.x reports 188.8.131.52x, but it doesn't have system_virtual_schema. Currently this will cause the schema parsing to fail, and the schema metadata remains empty.
SchemaQueriesFactory should inspect Version.dsePatch and use Cassandra3SchemaQueries for 184.108.40.206x.