If I'm trying to evaluate professors, it's a lot easier to see how well they write "G" than how well they educate.

Well, first of all, being a great professor has nothing to do with educating students effectively, it's all about research. Whether that's a good thing or not is a different argument.

But to take your argument at face value, chalkboard tricks can help you be an effective teacher. I think a professor teaching math without writing anything at all (and without slide shows or other visual aids) would be less than 50% as effective as normal, even if everything else was perfect, and I've seen teachers whose boardwork is sufficiently terrible that they may as well not write anything. Writing on a blackboard requires quite a few "chalkboard tricks", though a cursive G probably wouldn't be one of the more common ones. It is important, however, to cultivate a handwriting in which "z" and "2", "t" and "+", "w" and omega, "l" and "1", etc. are easily distinguishable.

Chalkboard tricks do not a great professor make. But I would expect that the correlation is quite high, considering the potential benefits.