Totally agree on the entropy @andy
This is why we are using both VRF and VDF.
VRF provide our weak entropy, which could be be biased with a withholding attack (a node can choose not to commit his randomness).
But as the VDF output is not predictable before the attacker eventually choose to withhold his VRF output, and assuming the VDF is a random oracle, both VDF output would be random.
Does that make sense to you?