I wouldn't say that they are weaker per level, but Deception certainly falls off really quickly after around lvl 40. Before that, the Deception tree gives you your basic tools faster than the other trees, but then doesn't have too much payoff.
The main issue for me comes down to us getting screwed by abilities granted from our tree. We loose 1 ability to our tree's charge while the other two trees just get to learn their charge from the trainer. So when we get Surging Charge the other trees get Dark Ward and Death Field. Both of those are pretty powerful abilities and it doesn't really seem like a fair trade. Further up, we get Low Slash which isn't the most useful skill IMO, I only ever use it to set up a Maul. Darkness gets Force Pull, giving it a 30m skill and another key tanking tool, Madness just keeps making Death Field stronger. Then the final skills, what should be the fruit of the tree, we get a slightly buffed Thrash that give Shock a bit of a boost... huh? Look in the Madness tree and in the 25-35 range their Thrash gets almost the exact same boost from Claws of Decay and Raze, maybe even a better one. Meanwhile, Madness gets another 30m DOT which also immobilizes, making it a beefed Low Slash and Darkness gets Wither which is a great skill.
The second is that our tree lacks survivability, Tanks are Tanks and Madness gets self heals and damage reduction and in return we mostly get better stealth. I like Stealth, but a lot of the high level fights are initiated by interacting with something and then fighting eliminating that bonus and if you Force Cloak everything not dead gets full health so it isn't that combat useful.