Hi,
In my testing for the scenario I label ‘pcloud virtual’ - the backup target was the pcloud virtual drive (by default drive letter P in windows explorer).
As far as I can see - the pcloud behind-the-scenes magic makes it looks like a local drive to duplicati so the numbers look pretty much the same as local backup and in the background the pcloud software would sync to the cloud (the backup computer can be the same running the pcloud software).
In your setup - you have two distinct machines right? backup computer running duplicati with the target to another computer (file server) doing the pclound syncing. In that case there is a slight difference as there is a network link in the middle and potentially that is the source of your different experience.