I'd just like to add that I left Toodledo years ago because it does not support sub subtasks.
I came back to this forum to see if that had changed, and I am disappointed that Toodledo still does not consider it important. Toodledo could be such a great tool if this single feature was added. It could, at minimum, be added as an option for those who do need it.
It seems that the solution to many of these issues are to allow nested sub tasks. Many of the suggestions here are workarounds for this main problem.
High level projects consist of many sub-tasks, which have their own sub-tasks, and a way to easily display this is needed in toodledo. This doesn't seem like it would be so hard to implement. Just allow every task to be assigned to a parent or a child task, and sort accordingly.