This may sound odd, but equating the visibility of a footprint to the damage done by that footprint isn't necessarily valid, is it?
My understanding of why steel spikes have been banned essentially everywhere is because of damage to the root structure of bent grass greens over and above the spike marks that knock putts offline. Take that out of play for both spikeless and softspikes, and you are left with compaction and disruption of the putting surface as the issues. Compaction should be a wash, or favor spikeless I would think.
As to the putting surface, in the case of spikeless shoes while the footprint might be more visible at first, the lasting impression should be less that softspikes, shouldn't it? I know that when I see footprints in a poorly raked bunker, the indentations left by spikeless shoes are easier to deal with than those left by softspikes; they are more regular and less deep. The idea of spreading the golfer's weight over several dozen points of contact instead of 8 or 9 is that each point of contact will be shallower, which should equate to less long-term damage.
Anecdotally at my club, more guys wear spikeless shoes every day, and the greens just seem to get better and better for it. But I could be wrong...