Maybe, based on HOW MUCH atemi/striking YOUR dojo/club uses, you should try training with a punching bag; then, after a while, your teacher and fellow students will tell you if your punchs/strikes are improving or not. Who knows, you may just get bored of training with a bag, but you wont know 'till you try it for a while.
As for whether or not aikido is "90% atemi" or not, THAT depends on where you are being taught. Under (like) 5% of the aikido I have been taught at my home dojo uses atemi. However, at other places I have gone to there is quite a bit of atemi. Aikido, I am starting to learn, is in the "Intent", not the mechanics or details.