I think the proper answer to your question is "Yes, you probably are," but only you know for sure. The benefit of the indicator vs. watching your line tip is distance. Imagine that your fly (the one being eaten) is the center of a circle. The smaller the circle, the smaller the diameter. What this means is that an indicator will go under water more quickly the closer it is to the fly. If a fly is 2' below the surface and the indicator is 2' from the fly, it will get pulled under immediately. If the indicator is 3' from the surface it will float for 1' before it gets pulled under. You get the idea. If you are fishing a 9' leader and the line is floating over the fly, it will float for 7' before it gets pulled under. While there are subtle changes that some fishermen can see without an indicator, the obvious dive of an indicator can increase the "set time" of most anglers. Of course this is a simplified version of the system, but if you want to dead drift a nymph without an indicator, you probably are. I personally do not use indicators, I know that I miss a lot of fish. I know that when I drop a nymph off a dry I catch a lot of fish that I would have missed without the top fly (indicator). I still fish without them cause I like it more. As I am apt to say, my opinion is free, and you probably got what you paid for.

One other thing. I think indicators could also improve a drift if it were fished like a dry where the visual of the drift can get rid of more of the drag on your nymph.