Training an elite marathoner is similar to chiseling a great statue out of stone. If you start with a perfect symmetrical pillar all you have to do is follow a certain formula of when and where to chisel and pretty soon the statue appears. There are a decent handful of coaches who understand and can implement some reasonable variation of this formula.
The problem is that the world is not full of symmetrical pillars. Instead it's full of rough boulders, lopsided rocks and strange rock formations. Unfortunately there are very few coaches skilled at the art of adapting the formula to these situations. It takes an intuition and knowledge and an art form to see what is the statue inside of each of these different strange but wonderful rocks and help release it.
We need more coaches who move beyond the formula and become artists, using their knowledge to help fill the world with beautiful marathoners, not just ineffectively trying to apply pillar formulas to oblong boulders. I think we'll find that these variations in rocks provide a wonderful diversity of marathoners. The question should not be "how to develop a great marathoner" but rather "how to release the great marathoner in YOU".