As an ex-programmer I understand what a bother progress bars are. Often you don’t know how long something will take until you do it.
Having said that, there are some places in Scrivener where the progress bars are quite inaccurate. One reason for progress bars is to let the user know that the application hasn’t crashed.
I now have 67,000 words in my document. When I choose to view the project statistics, a progress bar comes up and goes from 0 to 100% in less than one second. It then disappears, and nothing happens for five seconds. There is no hourglass cursor, and the numbers are all zero. Then another progress bar appears for a split second, too short a time to even see what it says. Finally, the numbers update.
My suggestion is to review a few of these types of things and find some way to let the user know that the operation is proceeding.
HTH,
Al