I think this is still true for the case of a conventional war. This can be checked in Ukraine right now. As far as I know, most of the losses of Russian troops at the beginning of the conflict are associated with hidden groups of Ukrainian soldiers who did not show up while the Russian tanks were making the initial march. And then, when supply caravans were heading to the front line, these hidden groups instantly attacked them from the side, and then hid again in the woods by the roads. Then the Russians changed tactics - no rush, but intense shelling of the front line with all kinds of artillery for several days, then a small advance, then a sweep, and then the cycle repeats.