I believe. I think the reason the apparent bedrock of the Columbia Hills are so shattered is the physical weathering processes (thermal cracking and separation) over so many eons. Even on Earth, when one considers all exposures of land, unbroken bedrock is relatively rare, and found almost only where flows of water or ice have given it geologically recent exposure. Broken up bedrock is much more common, and regolith or soils more so.

As far as the Gusev Basin material, I lean more toward the conclusion that this is a single unit of flood deposits. It is curiously unstratified, as exposed in Bonneville, such as a catastrophic flood might cause. Alternatively, as you describe, this could be impact ejecta infilled with windblown dust. I am wondering if there are good criteria to decide this, such as composition, size distribution or angularity. Unfortunately, since all the rocks have been exposed for eons to rounding by wind erosion, or made more angular by thermal cracking, any conclusions about angularity will be hard to support.