For the most part, I agree with what you're saying. The only problem is, "better" is subjective.

I've had cases where the person I'm working with can clearly explain why he feels one UI is better. And I was just as adamant about a different UI. I coded both up ways up, we played with both -- and we were still on opposite sides of the fence.

In this particular case, we ended up throwing both our solutions out the window and found something better, that we both agreed on. Unfortunately, it doesn't work out that easily.