I don't want to speak for the author, but I think it was an editing mistake. The way I think it was intended was, "The Soviets were willing to employ far greater cruelty, yet failed" - IE, the problem isn't just that we have pansy politicians back home, or are squeamish about doing what needs to be done; that's been tried against insurgencies and has failed at least as badly as any "soft" approach.
The Soviets in Afghanistan weren't the most vicious counter-insurgents in the world, but they certainly had fewer inhibitions, cared less about any internal or international pressure, etc. And the real point is - it didn't help. The way out isn't to "be tougher".