Partitioned parquet datasets sometimes come with _metadata / _common_metadata files. Those files include information about the schema of the full dataset and potentially all RowGroup metadata as well (for _metadata).
Using those files during the creation of a parquet Dataset can give a more efficient factory (using the stored schema instead of inferring the schema from unioning the schemas of all files + using the paths to individual parquet files instead of crawling the directory).
Basically, based those files, the schema, list of paths and partition expressions (the information that is needed to create a Dataset) could be constructed.
Such logic could be put in a different factory class, eg ParquetManifestFactory (as suggestetd by Francois Saint-Jacques).