"Could you twink out a fighter or rogue to be a better unarmored swashbucking type? Sure, but you wouldn't be a Duelist, which I think has a certain roleplaying flair." - StumpwaterJack
I'm sorry, but why wouldn't you be a duelist if you're a fighter/rogue instead of taking the duelist PrC? You can call yourself whatever you want. The problem I have right now with a lot of PrC's is that they substitute class for character.
You can be a fighter/rogue/monk, and be a Ninja. Heck, an 18th level straight-classed rogue can be a Ninja, and a feared one at that.
Class is not character. The point people are trying to make here is that the Duelist PrC actually seems to make a less interesting and playable duelist (small "d") than a fighter/rogue.
"That's not to say anyone's wrong for taking that position on the Duelist or any other class, but I don't personally feel that a PrC is wasted if it's combat effectiveness is slightly below the curve." - StumpwaterJack
That's not all people are saying. I read a TON of threads over the last two years about the 3.0 ranger. Too many. And invariably, someone stepped in and said, "But I had fun playing my elven ranger. It's not a bad class."
They missed the point. People complained because overall, the 3.0 ranger was a poorly designed class. People weren't complaining because it wasn't twinked out, powergamed, munchkined with all the trimmings. They were complaining because the class itself sucked, and sucked bad. I don't think the Duelist PrC is as bad as the 3.0 Ranger, but overall I am beginning to see a lot of threads pointing out that whereas 3.0 may have erred sometimes on giving players too much power too quickly, 3.5 may be falling off the other side of the log and taking too much away.