Check @TheRealSniker post today on the 1v1 tournament they just had over the weekend.
the runner up was a stamden and there are vids of the fights.
Stamden is mediocre at duels. It has things that it excels at and falls short to other specs in other regards.
Stamden excels at staying alive in duels, excellent class healing, sustain, tankiness in general via S&B passives, minor protection from ice armor and major mending after healing yourself with a Green Balance heal below 40% health.
It can turtle a fight very well and play for the long game.
It has phenomenal burst via shalks. Delayed burst skill allows you to combine it instantly with any other skill or ultimate such as DB or 2h ultimate. Stamden can seriously chunk someone when they want to.
The class lacks sustained pressure. Where it has great burst, it lacks in sustained damage via dots. The class does not have an in class dot or in class stun. This means it is not able to access DW for bleed dot because it will lack either a stun and reliable spammable if S&B is dropped for DW, or it will lack snare immunity, a good dueling execute and 2h ulti if it drops 2h for DW.
Both Stamina Warden and Magicka Warden are very predictable when they will be offensive. Shalks is very predictable and easily avoided by veteran PvPers who know when to strafe you, when to stun you and when to play defensive when you are ready to go offensive. Typically they will be offensive when you are buffing and defensive in the short window that the Stamina Warden is offensive.
Both Wardens have A LOT of buffs to keep up. This means they have a lower offensive window then other specs. A good dueler will take advantage of this and pressure you when you are buffing.
Easily accessed Major Defile and passive damage via bleeds/other dots counter Stamina Warden very effectively as well, which all of the more popular dueling specs have access to.
Over all, stamden is not bad at dueling and can surely do very well in the right hands, however the popular dueling classes right now (Stamdk, Stamblade) can shut down stamden very easily.