Of course it's a valid argument - you have to consider the costs and benefits of switching whenever you propose a change in a broadly accepted convention. For

Of course it's a valid argument - you have to consider the costs and benefits of switching whenever you propose a change in a broadly accepted convention. For example, one could make an argument that oral and written communication in the United States would be more efficient if everyone was forced to communicate in Klingon. But the switching cost would be so astronomically high that any possible gains pale in comparison. (I'm not saying the pi/tau cost/benefit is comparable to English/Klingon, I'm just pointing out that "that's the way we've always done it" is in fact a perfectly legitimate argument. The onus is on the person proposing a change to show that the change is worth it.)