Poisson Du Jour,
It is professsional to bracket! Absolutely. I've repeatedly told stories that I don't bracket, however it is for my personal work where one of the constraints is how much film I have.
One time I did a quasi-professional shoot of Italian imports (which I bracketed every shot). I gave the customer the selects. Now I accept on the surface your argument that alternate takes may be quite usable. But all I have left of this work is several slide pages of murky and overexposed garbage.
On one point I will dissent, compositional bracketing (or exploring, working the subject), is common and I think a good use of film. Here I try to improve on what I first saw. I'll take my first impression. Then refine by moving to a different vantage point. I'll spend more time on the second shot but often will not take it (the first is often the best).