When your talking about hybrids you expect something intermediate. With Mesopotamian you expect lots of points with webbing between with European you expect palmation. I would argue that deep clefts are an intermediate characteristic. I've read that some have argued that the presence of clefts in some populations of Australian fallow is due to Mesopotamian blood.
Personally I'd doubt that but it does interest me, if you could find the reference material you got that from I'd be interested to have a read. There is a book called "An Introduction to deer in Australia" which is what we consider our deer bible in this country and I don't recall anything along those lines from it but I'm always prepared to be proven wrong.
I still do think it's just a fault, similarly to how red deer can often be missing a bez tine (there are some people that attribute this to a theory that Sika and red deer hybridised when first released - which is just nonsense). In those pics you showed the antler length of the black and live bucks is short because they look like quite young deer. Our Australian deer e.g. reds, fallow, sambar are slow maturing and don't reach their potential until between the ages of 8-12. Genetics also comes into it though, some areas are just never going to produce good heads the same as some other areas always are going to.