The Self-hosted synchronizer is sequentionalsequential, whereas the cloud native Cloud Native one synchronizes items in parallel. This using limited degree of parallelism.
This means the Cloud Native Synchronizer is significantly faster that the Self-hosted one. It can synchronize thousands of items per hour, while selfSelf-hosted can perform hundreds of sync operations per hour. Based on the work items and issues size and complexity (number and size of attachments, custom fields etc) the speed of cloud native solution
Synchronization speed can vary based on a number of factors, see What are synchronization performance factors?
The speed of Cloud Native can be as high as 8000 items synced per hour, leaving self hosted solution an order of magnitude behind.