Red is better(or rather, more reliable/easier) than Purple, but Purple can be played quite well and hold its own against good yellow users and every other style, however it requires a lot more effort, probably the most in the game to get good at than any other style. I believe it has the highest skillcap in the game currently because of how underpowered it can feel at first against every other style and its very low margin for error, but the fact that its rarely used as well as its capacity for unpredictability and generating ACM from PBs can make it very powerful.
Playing purple against a good yellow duelist is like playing yellow against a good cyan/blue. Its rough, its annoying, and their halfswings get everywhere.
Against every style you will need a different approach/tactic.
The most important thing about purple is to yaw your swings as much as possible to speed them up. Not only does it speed up your swings, but it also makes them very hard to block consistently as long as you aren't doing the same combo over and over.
Purple also has instant counterswings much like red, but they are more dependent on a couple of a things: From which direction the opponent's next swing will come from (or how long it would take for their next strike to reach you) and how fast you are able to yaw the counterswing. WD in particular is really fast as a counterswing. Another very important skill to have when playing purple is to learn to read your opponent, more so than other styles because of how slow its swing windup is. This applies to both knowing when to attack or counter so you don't get interrupted, as well as reading your opponent's yaw'd attacks so you know where to PB.
If you are able to stay unpredictable with your combos and weave in halfswings and stab kata at unexpected moments you will be able to pull off some of the most satisfying kills in this game. Its a shame not many people are able to play it effectively, but that also speaks to the character of such players. Players that play purple are the masochist chads that really strive to improve themselves and enjoy the challenge of playing something more difficult than the norm.