Can a light be to bright for commuting? Yes.

However, I've been trying to find the best light (still looking) for this situation, and I've found there's at least 3 factors that seem to influence whether a light is "blinding" or not -
1. It's brightness - obviously
2. But it's only the amount of brightness that hits the persons face that really matters. A relatively narrow beam can work, and as mentioned some light even have an optically engineered cutoff, though that is trickier, requires more careful mounting and has it's own small drawbacks.
3. The size (intensity) of the light itself. I don't see this mentioned much, but I've definitely found that tiny and "kinda bright" lights can be really painful on the eyes when coming towards me on the MUP, but that larger lights that seem to be the same intensity aren't nearly as bad. I think a light that's a tiny point of light is more blinding that a much larger light with the same light output.