personally I think there is an argument for as you say a two stage exam system with the second stage only being able to be opened up when you have met the current ATPL experence level.
Then they can hammer you on all the stuff that really does kill you in commercial operations and stuff you need before going LHS. And have a rehash of the previous level to make sure its sticking.
And only after you have passed that set of exams can you sit the ATPL LST.