Just been looking at some video clips of STOVL transport aircraft developed 20-40 years ago namely the Vought, Hiller, Ryan XC-142, the Dornier DO-31 and the Fairey Rotodyne.
It would seem to me that the research gained from these prototypes would make a very good starting point for the development of a modern STOVL military airlifter that would have a greater range, speed and capacity compared to the current crop of, expensive to operate, heavy lift helicopters i.e. the CH47, CH53 and the Mil26.
Of the tactical transports you mention none really beat the performance of the C-130/C-27 class currently in existance. These planes can and do land on roads within a short distance from the 'front line' of our current war. What is needed is a newer generation Black Hawk or Lynx both of which are basic thirty year old technology machines. It is the High Hot limitation that is the problem in the current war, Until the introduction of the latest Lynx the RAF and RA were/are limited to the CH-47, which is too few and far between for the requirements being piled onto its worthy frame. (besides that at low and slow it is a Big Target.) What is needed is a more capable Helicopter especially in speed.
Other than poor high altitude hover perfomance the V-22 fits the bill, but at yw9ce to three times the cost of the Black Hawk or Lynx will there ever be enough of then for the delivery van requirement of the tactical company level helicopter. The STOVL transport is well served buy the current technology of fixed wing aircraft even the A-400. The Sikorsky X2 and the Agusta Bell 609 is where we should be looking.