Haha, they keep on moving that balance curve to be more and more geared for casual play.
If you're so bad at TF2 you have a problem with dead ringer spies then I dont know what to say. You just have to approach the situation differently than a normal watch, so the class is still grossly underpowered once you learn the tricks to a DR spy.
That's not the only issue with the DR. A staggering amount of spies are eschewing the other watches for the DR, that's a serious problem. The DR doesn't outright overshadow the other spy watches, but its ease of use/cheese factor makes it a blatantly better choice for most players, and that's not something valve wants to encourage.
In other words, it's a crutch for most players.