In this case the progress bar should show the percentage of processed data, but just using the amount of tasks or number of files is quicker and most often than not works fine
even then it would not be accurate, difference in file systems and storage medium would cause performance difference of processing many small files vs few large files. In TWRP when backing up, it would just straight up show you both progress and neither of them would advance linearly.
In this case the progress bar should show the percentage of processed data, but just using the amount of tasks or number of files is quicker and most often than not works fine
even then it would not be accurate, difference in file systems and storage medium would cause performance difference of processing many small files vs few large files. In TWRP when backing up, it would just straight up show you both progress and neither of them would advance linearly.