1. As already mentioned, it's working as intended.
2. It would be too OP.
3. Should the timer be increased to 12 sec or more you could juggle the stacks with transpose, could help the class, could make it OP, not sure.
4. Can't have highest ranged single target AND aoe.
5. All classes have useless skills. And just because you can't use some of them doesn't mean nobody can, Atherial Manipulation is great utility, for example it allows you to ignore some aoe and just teleport to you group. And both shields absorb what they should (Manawall can save you ass in A1S).