Parquet files would not be a good fit for your use-case of frequently modifying file contents because parquet files are immutable.

Meaning you would need to re-create the entire parquet file from scratch each time you wanted to "delete the data for user11" or make any other changes to the data. Making this file format extremely inefficient when data needs frequent modifications.

Parquet is more suited for bulk read/write operations where data isn't frequently modified.