It's because no one has the skills to complete harder mechanics at that point in the game yet. When I say skills, I mean abilities, not personal skill. The first dungeons only need dps because there are no tanks or healers at the level it is meant for, tanks for instance don't get their tanking "stance" until 14. Hammer station only just has healers and tanks with their most basic abilities, tanks for example have their stance and a taunt and that's about it. I haven't done Athiss yet but I would assume it is a continuation of easing players into their roles, actually teaching them how to play outside of saying "you're a healer, press 3 when someone gets below 50% health" in a tutorial tip. Saying that, it may scale slowly, and so have some more basic elements until the operations or last flashpoints but I think thus far it is doing it's job of teaching the players how to play the game in a group scenario.

RNG is RNG. I've had it with both, it's just luck of the draw. Same with particular gear types, belts I can't seem to get upgrades for at all after disassembling plenty of them but gloves I get first hit.