Howling:Cybermen development

I'd like to know how the Cybermen managed to improve themselves to the point of Nightmare In Silver. I mean, as the Tenth Doctor said to John Lumic, they're stripping themselves from imagination, and that's what they need to progress. However, with their wars with the Human Empire, they've improved themselves gradually to the point they became almost invincible to humans. How did they even manage to do so without imagination? --X29 15:39, August 14, 2014 (UTC)