I kinda agree with the OP, I think that Orca could be improved and made to be more acceptable. I think that most of the issues with Orca stem from the lack of administration features - the 'backend'. It's front end usability is not really so bad and can actually be made usable, with a few mods. (yeah yeah - we know - this should be core functionality).

I decided to stick with Orca on my site and have turned it into something a little better and more usable by adding in extra admin functions and see more a few font end enhancements, there's still a few more mods I want to do, but generally I prefer Orca as it is properly integrated and is nice and lean.

Whilst PHPBB and the others are definitely far superior products. IMHO integration into a dolphin site also brings a lot of unnecessary 'bloat', a lot of things are doubled up such as private messaging, avatar handling etc. This is not to say that one is better than the other, but for me the forums are not the main focus for my site, so the lean look suits my particular community better.

I think for sites where the forum is not the center of communications, Orca is fine, but for those sites where the forums form the main backbone of of what goes on, then something like PHPBB is a must, as there is every chance that you will lose users to another site with a better forum.