I think that you're making a fundamental assumption that a surface feature was created under the influence of only one factor; yet that can never be true of a planetary surface. There will always be physical molding from various forces like vulcanism and tectonics (not much on Mars) and subsidence and slippage etc.; the earth moves. There's a tenuous atmosphere, so features on Mars will also be sculpted by air flow. And many places on Mars have experienced the flow of liquids, and I think this is one of them.

Thank you for the large-scale overview. It shows what looks very much like an alluvial fan at both ends of the rille--fluid flowed there. It may originally have flowed through the original lava tube, which over time may have eroded the roof. (Or may have come after the collapse; enclosed flowing liquid is not crucial to this scenario.) After it collapsed, the fluid swept the debris on down the channel and out on to the plain. That's why the floor and walls are relatively smooth (I'd also posit wind softening the jagged upper edges; or flow over the edges when there was fluid on the adjacent plain; the overview also shows the rille at the bottom of a valley). Contrary to your later statement that purported lava tubes lack openings, the large-scale image clearly shows both ends open.

It seems to me also that a collapsed lava tube is a plausibly straightforward and simple explanation for the existence of a "bridge". The roof didn't collapse there. Why did the hypothetical electrical arc scour the entire channel but skip that one spot? Your hypothesis would be stronger if there were multiple arches supporting the "stuttering" arc description.

Doesn't work for me, Michael. Sorry.