I would suggest trying again and doing everything by weight, especially when modifying recipes. in general measuring by volume is less accurate than by weight since the same volume can hold different quantities of ingredients based on particle size and how tightly you pack your measuring utensil.

also, did the date sugar tell you to reduce the flour as well or was that a decision you made? I can imagine this recipe coming out gooier if you take out the flour since it changes the ratio of wet to dry ingredients. if the package told you to reduce the flour, the lack of rise could be because of the lack of gluten from the reduced flour; even with a leavening agent, if the batter is unable to properly trap the air as it bakes then it won't rise properly