Both the oil and the yogurt are helping to make these cake-like. The easiest fix might be to find a different eggless recipe which calls for butter (or shortening of some kind) and no yogurt. Maybe look for "ginger snaps", and if you don't want the ginger you can leave it out. I'm pretty sure ginger snaps without the ginger would have to be called "molasses cookies". The following will probably get edited away since exchanging recipes seems to be a no-no, but I did find one recipe here http://www.spiceupthecurry.com/eggless-gingersnap-cookies-recipe/#wprm-recipe-container-26703
If you want to tweak the recipe you have, my first recommendation would be to substitute butter for some of the oil. Evidently you are open to a little experimentation since you already modified the sugar quantity.
Which brings up sugar quantity: not sure if you want "less soft": brittle and crispy ? -- or "less soft": hard ? White sugar promotes the brittle and crispy characteristic, and flour promotes the just-plain-hard characteristic. So if you want crispy and less sweet, maybe removing some of the molasses would be better than removing white sugar. Losing some of the liquid from the mo. in the batter might also help with getting them less cake-like.
I have made ginger snaps that came out real hard and clunky (sort of like the cheap ones in the box at the supermarket) just by putting in a little too much flour. If that is what you are going for, a little more flour is your answer.
Keeping the cookies in the oven just a teeny bit longer can also harden them up a little.
Of course changing stuff will require a little trial and error to get a good balance, but keep an eye on the dough as you tweak things to make sure the consistency remains reasonable. If you already decided to go ahead and halve one of the ingredients just to see what happens, then it sounds like you are ok with experimentation.