Not necessary, medium format manual camera enough. Large format just introduces additional weight and bulk without teaching additional skills about photography.
Look-- like it or not, tools define how we approach a craft. For example, when I go to model shoots, inevitably I'll see the DSLR users firing burst modes once the model has struck her pose. 10, 20, 30 shots a pop. And they keep doing it pose after pose. This is not sports, not action-- why are these guys shooting burst? Simply because the DSLR's already changed their belief from "make every shot count" to "free what". A film camera user would never do that, but DSLR's have changed everything. So the art of the decisive moment is lost.
Some people think that a camera is just a light tight box, but I've already written on the how illusory that logic is. The fact is that automatic SLR's/DSLR's make it easy for photographers to be lazy. Technologies such as 1000-point autofocus, matrix metering, sophisticated automatic flash/fill-in flash, VR/IS zoom lenses, burst mode, clean ISO 3200/6400, Program Mode, etc. all try to take the thinking out of photography.
But look in the Portraits & Poses section, what do you see? Tons of well-exposed, properly flashed but totally flat lighting, perfectly sharp pictures all with the same perspective-- all perfectly boring, all with unreal perfectly PS-ed or over-PSed porcelain smooth skin, not a stray hair to be seen.
Look in the sports/reportage section, what do you see? Tons of well-exposed, properly flashed, perfectly sharp pictures and perfectly motionless pictures-- runners stopping in mid-air, concert performers with mouths frozen open, all zoomed in, all perfectly unnatural.
Why? Because the photographers have let the DSLR's do the thinking for them.
Look at the great portraits. You'll find many of them used natural light, they knew how to use light and shadow to create a mood, they did not always have everything sharp (and in fact, were better off that way).
Look at the great sports pictures. You'll see lots of motion blur (exactly what DSLR's try to avoid), very little flash but great perspectives-- over, under, in the field, etc.
Yes-- some people will say that a tool is not responsible, if a photographer is lazy, it's not the tool's fault. I disagree. A manual camera makes one work for the picture, and it can only be better for the development of the photographer. Those who start out with DSLR's have a tendency to be lazy. It takes a very strong person to want to learn how to turn off the auto programs in a DSLR so that their pictures will stand out from the thousands properly exposed, perfectly sharp and perfectly boring shots.
