Its very doable. Concealment is not a bruteforce class and it has a higher skill cap, in my opinion, then the other classes. You will need to use your Crowd control abilities on some pulls, and not on others. You need to see what abilities your companion has and what they might do (break CC) etc. I use Kaliyo as a tank and can kill same level elites without an issue. For act 1 end boss, make sure to use your shield and interupt his casts with your interupt and you should be fine. follow a good dps rotation and use your stim boost. If its going to be close, corrosive dart him, then line of site him (he cant use ranged abilities if he cant see you) and heal yourself. Use your energy cooldown when needed. Use your stun early in the fight so that it will be back up later for you to use again. Use it as an interupt and not just randomly so that you can interupt more then one spell every 12 seconds etc. There is lots to do and lots of options. It makes it harder to play the class but played well you can do some amazing things.

I was hoping to find some revelations here but not much. I'm a 37 concealment OP and find Kailyo to be the best. Your best damage is with backstab in the rotation so you want the back of the mob. Her AE threat is good and if you use your stuns and interupts on dmg casts she can tank elites without an issue. Don't forget that you can mount up and then dismount and she will be back at full health. She takes all the damage and you're ready for the next fight after a fast mount/dismount. I'm eager to see how Temple and Scorpio end up.