Wobbling on the stand is completely unacceptable. Something's bent. The only difference between Sora and, say 105, is that Sora is painted and 105 is anodized. Maybe a slightly better finish, but Shimano doesn't tool up for 4 levels of crank- they just spend less time on the cheaper ones. Drop forges and dies are pretty darn expensive, and if you can use the same forge for 4 different cranks, then you're way ahead. The first hollowtech cranks were the top of the line Dura Ace, then they did cost reduction to Ultegra, then 105, then Tiagra and Sora.