1) If everything worked as well as you think it oughta, trappers would be extremely frustrating and possibly OP. If you had to constantly worry about hitting knockout traps and going to sleep for hours at a time, with no risk to the thief in question, it would be a nightmare.

2) Nerfed as they are to counter the above, they are basically unplayable unless you are going for the RP of it. Any other thief path completely outshines them. I did it with a duergar, got decked out as much as possible, and at the end of the day I was a punching bag with a lot of very unreliable abilities which took a ####load of time and effort to employ (prep gathering).

It makes sense for trappers to be around, from a thematic point of view. However, it is not possible to keep the path balanced whilst also maintaining a reasonable degree of enjoyment. I think the path should be scrapped and have the skills used for flavor throughout the game for NPC's/areas. That, or get rid of the most worthless abilities in the path and put the rest in a mini-path, like the arcane and locksmith paths.

My trapper thief was, without a doubt, the most maddeningly horrible build I have ever played. Followed by my Mundunugu, Ghriz. At least you get bash + savage feeding with that. With a trapper thief you are basically a joke who only manages to be annoying on a really good day.