People aren't used to this Thief in Eden Eternal. Like the other guy said, Sonic Cut stacks as your "poison" equivalent. The Sneak (your infinite stealth) is crippled since you can't use it once you enter battle, but it's good for avoiding battle at the start of a duel so that you can start the fight on your own terms and psych out the opponent (you see a blur, they see NOTHING). Your buffs are the quickest to cool down compared to other classes, so you can constantly have your Agility and Eva buffed up. Special item called Tindolos's Broken Skull, which is my best weapon since it increases the duration of Gallop by a full ten seconds. You get 25 seconds of active Gallop, and the 15 second cooldown is overlapped so that it's really only a 5 second cooldown. Even if you do not fight, Gallop adds a handy 36% running speed if you pour a Knowledge Point onto it's skill on your skill tree. With all my other gear, I end up sprinting at 66%-76% speed depending on what I'm equipped with at the time WITHOUT a mount. Yeah, I pass a lot of people on shining alpacas and razorbacks (my cheap alternative to actually getting one of those cool mounts).
Anyway, Martial Artist does a lot more damage than Thief, especially within a time frame of 20 seconds. Like, insane damage. Thief can burst very quickly, and do many bursts, but is totally overshadowed by MA in straight up damage. The only thing Thief has over MA is stealth, and Eva. They are Eva masters, striking 100% easily (you can still get hit at 100% Eva, though) making it really hard for people to even land a hit on you. You're in trouble if your opponent in PvP has over 500 Acc, but you're safe if they have under 300. Be a good Thief and scout your opponent's stats before accepting a duel. Basically, MA tries to pound the opponent before they can land a hit, and Thief just stops the opponents from being able to land a hit. Use either one right and you win. Get cocky with MA and you get smacked down or sniped from a distance. Overestimate your Eva with Thief and you fall like the squishy class you are.