Self-hosted synchronizer is sequential, whereas the Cloud Native one synchronizes items 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 self-hosted can perform hundreds of sync operations per hour.
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.