Having an open center without question allows for maximum light penetration and highest fruiting within this scaffold area. The issue as I see it is that this space becomes your cropping limit. A true central leader tree, particularly on the more vigorous stock, allows many scaffolds, and thus a considerable higher cropping potential. Certainly there is greater shading within each scaffold than you would find compared with open center, but you get more of them. Many growers in Europe and in North America traditionally went for these forms for ease of management (like spray coverage efficiency). But for highest yield, per tree, a larger central leader with multiple scaffolds wins out, especially for cider production.
The other issue is tree strength. A branch obtains some strength from the overlapping sheets of cells when both trunk and branch lay down their secondary growth each year. When trunk is absent above a branch, as in open center management, the branch stability is compromised. This doesn't necessarily spell disaster, but it certainly increases the possibility. Cropload, snow, etc, can tear these branches like a peeling banana in my experience. So, if folks are experimenting with this method, a subdued central leader without additional scaffold branches should be allowed to grow to strengthen the sidebranches below.
The bent leader is usually the result of leader cropping. Most suggestions are for the leader to be stripped of fruit to disallow this. It does, however, subdue the vigor, keeping the tree lower without cutting that leader. If allowed to grow too large, it of course shades the tree, but we are not supposed to allow this to happen.
A point I like to offer to folks these days is that the tree is a pretty nice vehicle to effectively increase food and organic matter production in the landscape. It beats all other forms of vegetation simply due to its aerial space occupation. By letting a productions system like the tree explore a maximum area, we increase production. This includes the crop of course, but it also mines nutrients from air and soil and deposits them as litter and prunings, thus increasing topsoil, mulch, and btu's for the farm. A plant, be it an herbaceous species, or tree, is quite limited in these possibilities when it is forced to maintain a particular height.
So, with proper management, there are probably hundreds of systems, the open center included (look at what the Japanese were doing in the 1800s with their high density opencenter production if you want to see something really cool), that can be done in a satisfactory way. If an orchardist is willing to take the extra time to monitor for potential breakage, because they want ease of spraying and harvesting it makes sense in the same way farmers engage in the upfront costs and management particulars of high density trellis growing. But, for maximum production of organic matter, carbon sequestration, wildlife habitat, minimum ammendment input, and yield per tree in the ground, the larger sized central leader tree is the best option.
Walden Heights Nursery & OrchardZone 3 in Vermont