This is not what my experience shows and it certainly would negate the use of a densitometer as a tool for greater accuracy. In my negatives both developed in pyro or pyrocatechin the stain makes a great difference in the density of the highlights and is certainly greater than 10%. For example negatives developed for a DR of 1.5 for pd printing show in vis light a max density of 1.2 but with the blue channel they show 1.5 sometimes even 1.6. This is 1 stop in exposure and approx 25% of the DR, certainly far greater than 10%.
Originally Posted by Loose Gravel
If one is working with normal enlarging paper, I agree that the UV spectrum makes little difference, in addition enlargers put out very little UV (the reason why they cannot be used for alt processes) which is mainly absorbed by the lens. But if one is working with an alt process or azo, the UV spectrum is very important as it is the part that exposes the medium.
Testing can be made as difficult or as simple as one wants but the more involved testing procedures with use of a densitometer produce the best results. Sensitometry for photographers is not difficult and it certainly produces better results than "take a pic and see what happens" for that I agree you don't need a densitometer, you do however need a lot of money to buy lots of film for the trial and error.