Grant was average after Yates left, not poor. He has proven that in a team doing well in L2, he can be a real asset. Mansfield are a team doing well on L2, and I expect Grant will be the type of player to push them over the line into automatic promotion contention.
As someone else has said, Mansfield have strengthened in the January window during a promotion campaign. Imagine if we'd done the same last season. Instead, we lost our best player and signed a couple of no-hopers. That's the different between the two clubs - one makes the right decisions, the other doesn't.