You're right.
But until stalkers up their game with regard to carcass presentation, there is no hope of an increase in prices.
Currently, the carcass price is pegged to the lowest common denominator, and the stalkers who do submit good carcasses are subsidising those who don't.
The price you suggest is about right, in my opinion. I can pay £4/kg for a good clean fallow carcass, and still make a reasonable margin on it. But it's got to be head shot.
Were you the chap in the hat who made this point (almost word for word ) at the stalking show panel discussion last Sunday? If so I was sat just to your left.
I broadly agree with you, it feels to me a bit like the sport of stalking is in a state of flux. There seems to be a traditional expectation (that was maybe reasonable in the past) that an amateur stalker can expect to stalk at their own pace, not pay (or pay very little) for the privilege, and offload excess carcasses to the game dealer at a sufficiently good price to cover a large part of the costs.
In today's world that seems unrealistic. If you're stalking for fun you're probably going to have to pay for it, either in cash or graft/time (e.g. serious doe culling to earn the right to stalk summer roebucks.)
If you want to make money selling venison you probably need to treat it as, at a minimum, a part time business and be professional about it. You probably also need to accept the reality that acting solely as a 'resource extractor' is, as in many industries, less profitable than vertically integrating and providing a product to the final consumer. Value gets added along the processing chain and, rightly or wrongly, the bulk of this isn't at the stalkers end, and that's unlikely to change. (see 'farming and supermarkets' for further details of this intractable conundrum!)
If you're a landowner who wants serious culling done, you're probably going to need to enter into a transactional relationship with someone who is making money off getting the job done. This could be straight up contracting, guiding (alongside meeting cull targets), or venison production. If you're a stalker who is being asked to do serious culling, you're almost certainly going to want something in return for the time and investment in specialist kit required. (Argos, larders etc etc)
Obviously there's scope to combine some of these strands together under certain circumstances, but that feels increasingly like good fortune rather than a reasonable expectation.