I agree with half of your post. Semien had a paltry 326 mediocre plate appearances across 1.5 seasons in a White Sox uniform but his minor league offensive numbers were very good for a middle infielder. The Sox traded him at 23 years of age. There was plenty of time for him to pan out, just like he did.
However, the Sox failed to recognize that Semien was a better talent than the bum starter they acquired with only one year of control. This is the problem with the trade, just like the Tatis Jr. trade.