One of the criticisms I've heard about the recent Star Trek: The Next Generation/Doctor Who: Assimilation2 crossover is that it made the Cybermen too powerful, that they were never that dangerous in the TV series. But then "Nightmare in Silver" was made, and that had the last war with the Cybermen necessitating the destruction of an entire galaxy to stop the Cyber-threat. Does this make the plot of Assimilation2 any more plausible?
Assimilation-Squared has many problems and many legitimate reasons for criticism, but I don't remember the Cybermen being too powerful one of them. Some might have taken issue with the Borg being so easily defeated by the Cybermen, but that's more related to the Borg being presented as too weak than the Cybermen being too powerful. Personally, I had no problem with the Cybermen totally overrunning the Borg, but hey.