PDC or BDC which takes the heat?

I have a PDC that’s runnung SQL, providing all network shared printers, running DHCP, hosting an HR application, and is the mail file server.

I acquired another with the intention of making it the PDC to take the heat off the SQL server.

Some folks have told me yes, promote the new server to become the PDC and others have said that it’s the BDC that does all the work.

Can you tell me which is true??

Thanks,
Jim