Well what I think the Reno brothers did was take any code they could find that made sense within the TF concept and build a TF style game that valued short/long range classes, special abilities and ways to undo or dodge those so the whole concept got depth and selecting classes was interesting for each map.
When you read the TF documentation on planetfortress you will find much of it made a return of some form in WF. For this they indeed didnt need to listen. The tweaking of classes was however done with listening to the community and by playing. Of course 3.0 resulted in the obvious peak in community and gameplay in version 3.3 where some extremities from earlier version got corrected.
From version 4.0, WF got a steady fleeing of players even more encouraged later by the MOCK mods that took over several servers.
In the end, I think their succes was to stick to a good concept and making sure every class and function added fitted that concept and contributed to more interesting teamplay. With 4.0 and also with WFA, I think some of that focus got blurred and resulted in a smaller and smaller community despite the growing worldwide online community. Let's hope WFR will find the way up.