I disagree. If you can't rate/measure the surface and compare it to other surfaces then how do you know what the potential impact is on horse health and safety let alone performance?
How do you know that the Cambridge track was laid to the correct specifications and is behaving as per specification unless you measure it? Will the Riccarton one behave differently to the Cambridge one? Can you alter the surface hardness by doing the grooming differently, less or more regularly or consistently across the entire course? Surely "hardness" can be measured? Actually it MUST be measured from a health and safety perspective.