rclone can indeed be significantly faster than the native OneDrive client when transferring data to and from Microsoft OneDrive, primarily due to its multi-threaded capabilities. Here's a breakdown:

Multi-threading with rclone:

Concurrent Transfers: rclone is designed to perform multiple file transfers simultaneously.¹ You can control the number of concurrent transfers using the --transfers flag. This allows it to utilize your network bandwidth more effectively, especially when dealing with numerous smaller files or when your connection has high bandwidth.
Multi-part Uploads/Downloads: For larger files, rclone can break them down into smaller chunks and upload or download these chunks in parallel using multiple threads (--multi-thread-streams). This can drastically reduce the overall transfer time by maximizing throughput. The --multi-thread-cutoff flag determines the minimum file size for multi-threaded transfers.

Native OneDrive Client:

The native OneDrive client, while convenient for continuous background synchronization, typically operates with a more conservative approach to resource usage. It's optimized for reliable, steady syncing rather than outright speed in bulk transfers.
It might perform some level of concurrency, but the degree of parallelism and the control over it are far less than what rclone offers.

Why rclone can be faster:

Control over Concurrency: rclone puts you in control of how many simultaneous connections are used, allowing you to tune it based on your network and system resources.
Optimized for Bulk Transfers: rclone is built for various cloud storage interactions, including efficient bulk uploads, downloads, and synchronization.
Less Overhead: Being a command-line tool, rclone might have less background overhead compared to a continuously running GUI client.

However, it's important to consider:

OneDrive Throttling: Microsoft OneDrive, like many cloud storage providers, can implement rate limiting or throttling, especially with high usage or a large number of API calls.² Using a very high number of transfers with rclone might, in some cases, lead to temporary throttling from the OneDrive service itself. It's often recommended to start with a moderate number of transfers (e.g., the default of 4) and adjust based on your experience.
Configuration: To achieve optimal speeds with rclone, you might need to experiment with different parameters like --transfers, --checkers (for checking file integrity), --multi-thread-streams, and --multi-thread-cutoff.
Initial Sync: For the very first large sync, rclone can be significantly faster. However, the native client excels at efficient incremental synchronization after the initial setup.
Real-time Sync: The native OneDrive client provides real-time or near real-time synchronization of files as they change, which rclone, being a command-line tool, does not do automatically in the background unless you set up scheduled tasks or use a mount.

In summary:

For bulk data transfers to and from OneDrive, especially large amounts of data or a large number of files, rclone has the potential to be much faster than the native OneDrive client due to its multi-threading capabilities and the level of control it offers over transfer concurrency. However, be mindful of potential OneDrive throttling and the need for proper configuration. For continuous, real-time background synchronization of a defined set of folders, the native OneDrive client is generally more convenient.