The one certainty in this is that Packham is not operating constructively, but is grandstanding in a confrontational manner for his own personal gain. His article was ill-informed, quite likely spurious and frankly silly. His argument for Dartmoor being overstocked consisted of noting that grazing densities were lower in the Lake District, a region both much further north and much higher than Dartmoor. There is no reason to suppose that the productivity of the two areas are equivalent. He blamed the state of bogs on peat extraction, which is either very, very out of date or wrong. He made no mention of the increasing erosion and other damages caused by ramblers and other plastic shedding lefties all over the moor, nor by open public access, poor policy from the park authority and so on.
Dartmoor National Park is badly managed and sheep are a small part of the problem, people are a large part - particularly activists.
The fact is that people like Packham neither like nor understand moors and particularly dislike the traditional ways of managing them and would much prefer them to be re-engineered into boreal forests.