Well put, I admit some of my love for the frame and my imagination running overboard has swayed my opinion, but what I'm understanding is that you would like to see what's best physically for Atlas, not what could be best with the community and it's interactions with Atlas.
For example, your idea of a rumble dome, although interesting, would be a bit of an eyesore to other players. Remember how people complained (and still complain) about Frost's snow globe taking up too much room and impeeding other players? Well I'm sure that would also get picked as annoying by others.
The fact of the matter is, the ability needs to be synergistic to the frame in question without hindering both itself and others, and if it's an augment, provide some form of different playstyle which gives trade-offs that are equal or greater than the demerits it applies.
Otherwise, from what your saying, it sounds as if Atlas's Rumblers were a bit more aggressive you would be fairly happy with the ability.
In terms of Rumbled, Ive played a lot of games which have abilities that provide negatives with beneficial positives. So for example, if Atlas uses Rumbled as it is, (not being able to parkour, use guns, etc) he should gain positive effects that would outweigh this detriment. Examples being heavily increased armor, access to an area CC, access to a ranged AoE, immunity to CC, the list could go on.