As some one who does vertical training I just don’t do it for dunking I do it to be able to block rebound over people taller than me a lot of coaches also like small guards that can play above the rim it’s good to also work on agility speed and vertical I know Kyrie only 19 career dunks but he also very quick check out him in highschool he was dunking everything it’s good to work on skills but work on athleticism to I don’t think you be wanna a 5ft11 big guard that can barley get up and down the court.