The correct service provides a fully managed environment to perform the ETL (Extract, Transform, Load) jobs necessary for converting the dataset from its current format into a more efficient columnar storage format like Parquet. This choice allows for the automatic scaling of resources to manage the transformation tasks, which reduces manual oversight and optimizes costs associated with running large-scale data transformation jobs. Amazon S3 is primarily a storage solution and doesn't have in-built data transformation capabilities. Lambda, while capable of running custom code to convert data formats, would involve a higher management overhead as it is not specifically tailored for ETL. Lastly, Kinesis Data Firehose is designed for real-time streaming use cases and not for batch transformations, making it unsuitable for this scenario.