Another problem with Heroes, which was evident in s2, is that they changed the plan at the last minute and the show suffered for it.
They were supposed to have a mostly all new cast for the next season, focusing on a whole new group probably in a different part of the world with a whole different set of powers. It was supposed to be a brand new story that would possibly all link back together at some point.
S2 was stupid, pointless and went in a circle that led right back to where it started. S3 had a few moments, and by the time it got interesting again in s4, it was already too damn late.
and yes, the show that needed a late revival was Firefly. But everyone from that has moved on and Joss is busy doing Billion Dollar Movies now, so that won't happen.