Plance has hit the nail on the head, when he says,"...Now...valuable Topic threads are buried amongst perhaps thousands of Topic Replies...This degradation of categorization is a profound disservice to the functionality and lifeblood of our forum..."
This is exactly the problem. What you've done here is the equivalent of having a nicely organized filing system and taking all the files and dumping them into a single file folder. I'm sure you don't have your in-house computers set up that way. You have them organized into drives, folders, and files that make sense and allow you to do your work in the back end of the system efficiently. Why can't we - your customers - enjoy that same level of organization on the front end?
I really hope you reconsider this ill-conceived change. The functionality of our forum has been severely "deprecated" because of this.