Katanas, and curved swords are weapons that are widely used because of their extremely shallow learning curve; they're weapons that require not much in the way of investment (time and stats) to use with a certain degree of efficiency.
There are plenty of weapons that share this trait. Weapons such as the MSGS, zweihander or blacksmith hammer, (none of which regarded with the same animosity as katanas) are all weapons that require little invested time and stats to use well enough to reach standard skill* with.
*Standard skill is how I refer to one's ability to surpass the minimum of a 50/50 win loss ratio, while utilizing the entirety of their weapon's move set.
Some weapons, however, require some dedication to reach standard skill with. Weapons such as the murakumo, flamberge or lucerne. All weapons are very viable, but can be disregarded due to reasons such as awkward timings, or unforgiving stat requirements. People who use these "Advanced" weapons at standard skill level are *usually* regarded as pros, or good players.
The weapons mentioned are entirely my opinion of course. Which weapons do all of you deem "Advanced" weapons, and why?