I mean the same type animals with different quality should have different speed, power, hp pull, etc. This is a quite obvious idea: more valuable thing should be more difficult to obtain. I'm surprised why it is not so. If there is such relation, it should be increased, because nobody notice it.
I do not think that it makes hunting more difficult for most players, because of exploits. But at least the high-quality animals will take a little more time and will be more dangerous for accidental death during hunting.