Trading for Reggie Jackson would have been a perfectly horizontal move.
The problem is that we didn't want to sign an expensive contract for a disgruntled, ball hog, low team chemistry, no defense, me-first player. We weren't going to sign Enes Kanter. Reggie Jackson was equally disgruntled, low defense (perhaps not equally, but close), ball hog (needs the ball in his hands to be effective), me-first player who was going to require a large contract.
Sure, on paper, Kanter for Jackson looks like a lot more value than Kanter for a 1st round pick and a German long Bratwurst with Gingerpubes on it (Pleiss). But, it would have been horizontal since we would be in the same position. The trade we did netted us something for Kanter. PS. Kanter STILL doesn't have value. OKC wanted to trade him all summer, but couldn't.