Les, in what context do you say "it's the hardest of all clay disciplines"? I would argue that ABT is "harder", as in it is compleatly random without a computer program to give everyone the same 100 clays, each peg has a different hold point requirment, unlike OT where the hold point is the same each peg...
OSK is another candidate for being harder...some people can just never adjust to shooting gun down at very fast crossing targets, with doubles thrown into the mix, with only one shot per clay...how many OT pairs do you get per round?
The mixture of skills, memory bank of angles/leed pictures/wind affected calculations and mental stamina required to win at a shoot like the GB FITASC shoot held at Westfield, with 136 different target presentations is far,far more complex than 5 pegs of fast, going away clays, all with a centeral hold point, repeated over and over?!?!
I'm not a "trap" shooter, I have shot very little registered DTL or ABT only shot 'competitive' OT once at a charity A/R shoot, 21 ex 25, I have shot 25 DTL, 25 ABT and 25 OT as practice a few times on a wednesday night @ North Ayrshire practice (usualy because it's wet and the trap ranges at NA are covered!) I always find ABT to be the harder of the trap disciplines!!! I've shot a round of OSK or two with the boys who shoot it...there is no second barrel, the 3 second delay takes some getting used to, not easy, less so with a 32" sporter, esp if you've got 1/2 1/2 choke in (was too lazy to change).