Your first plant looks like Mystery Day. Can't remember if I've ever grown that one so I know very little about it. Dahlias have different characteristics, sometimes even among the same variety. I've grown Otto's Thrill for years and have no idea why it produces so few leaves. The plant in the photo had 26 6-8" blooms at one time, with hardly a leaf in sight, except down toward the bottom. I wish there was a better proportion of blooms vs. leaves but if given an either/or choice, I'll take the blooms every time! If I were you I'd enjoy the beautiful blooms and forget about using fertilizer to try to alter anything. Best of luck with your second plant!
Otto's Thrill
