The biggest problem I have is with the notion that a variable can be considered in isolation. Take the idea that you can mash for 30 minutes, you can but that will change the nature of your wort, Beer is a natural process that almost wants to happen so that one change may not have a big impact. Do a 30 minute boil again in isolation it might not have a big impact on a well mashed wort.
BUT - do both together and the "Minor" changes accumulate, the beer will be noticeably different - the old how many corners can you cut off a square before it looks more like a circle.
Same applies to every step in the brewing process, they are all interdependent the finished beer is the culmination of all the ingredients and processes used during its production. Or as I have said before - everything you do ends up in the glass.