After looking at the results of the men's and women's 5K semi's, its seems to me the system is unfair in that it greatly favors the second heat. I say this because all the qualifiers come from the second heat in both fields because they know exactly what kind of time/splits to hit based on the results of the first heat.
The 5K is nothing like an open sprint or relay where you can control your time with any kind of distinct accuracy, so the arguement that its the same for every event doesn't hold water in my opinion. And if someone says the first heat should know better and that they should just run harder isn't realistic. Perhaps it should only be top 7 runners (or whatever) per heat.