This season Idah has a minutes per goal rate of 204 minutes in the Championship, with most of his appearances coming off the bench. Kone's rate is 386 minutes, almost double Idah's, while playing for a team that scores more goals than us.
We are lucky that Vipotnik has done so well this season, but it's not hard to imagine that a guy who scored 20 goals last season in the SPL and Champions League would also have scored a good amount if he was starting regularly.
The desire to write Idah off from day one only makes sense if the person doing so is a Rangers fan. Otherwise it's baffling.