I know what you mean about differences in Tai Chi. I was watching a class yesterday, and the instructor "held the ball" so I could almost (really) see the energy between his hands. Some students were trying to do the motion as if they sort of knew what was going on. One of his best students had the motion down, but there was no energy. He was striking a pose, really, not building for a strike.
It's the intense focus that I love in aikido, and I think it's the heart of good tai chi. But I am certainly talking off the cuff, as I have never studied it...