With the latest version of PAC CLI, there appears to be support for parallel thread processing: ( https://learn.microsoft.com/en-us/power-platform/developer/cli/reference/data#--connection-count--c )
Surfacing this as an optional parameter through GitHub actions would be a significant improvement as the current approach runs on a single thread, making it process very slowly for larger datasets. (alternately, defaulting to a higher number than 1 would also be helpful).