This has almost certainly come up before, but it seems worth repeating.
Bomber armour and helms, whilst providing variety in their bonuses, seem to ALL be split Normal/Elemental defence (unless the wiki's out of date). Where's the Shadow or Piercing armour for bombers? Are Three Rings saying that bombers have no business fighting anything other than gremlins and constructs? What gives?
I understand that a good bomber avoids damage rather than absorbing it, but the same goes for gunslingers, and they get a choice of Piercing, Shadow or Elemental 5* armours. Surely it's not too much to ask to add a couple of new sets to address this?
I can not speak for other demolitionists, as I rarely end up in a party with others, but I believe it is due to the dodging abilities assumed to be mastered by the user. Pierce comes from the Beast and Jelly families, which are fairly easy to dodge. Shadow comes from the Fiend and Undead families, where the only difficulty to dodge being hit comes from Devilites and Greavers; both are destroyed by foil/rapier swords. Element is inflicted by the Gremlin and Construct families. Gremlins in T3 are sometimes difficult to dodge. Other than that I do not know why the demo set lines only have element defense.