It doesn't matter which generation you put Shaq, Duncan is still the overall better player. People are still living off the memories of "peak Shaq" and wrongly rating him on his offense dominance only, as old media type of fans (like Mitch) tend to do. Indeed, Shaq was a tier above Duncan in scoring, but Duncan was tier above on defense. Duncan was also better at the "little things" like pick setting and adjusting to game conditions. Their passing out of double teams and to cutters is about even, but Duncan is a much better outlet passer.
The two players are close, but Duncan edges Shaq out as the more complete and effective player.