Well it kinds of contradicts, because prime is wise and has been with the matrix, and he chooses who to take the leadership. So technically you be saying prime has poor judgement. As he chose Magnus to lead and hold the matrix it is relevant as he did not expect hot rod to lead.
You cannot say Magnus was not at all worthy or he wouldn't be carrying it for the autobots regardless the matrix chooses to open.
Arguably, it was just not the darkest hour.
I am not going into this debate. Yes he can't open the matrix, I will stop there.