If you dont use your muscles, then you cant move your body, let alone throw anyone. in my humble opinion aikido does use strength, its just srength focused onto one particular weak point of uke's body to gain maximum effect.
Bigger stronger people generally tend to have an easier time of it too, they can meet an attack head on and go through uke, whereas a smaller lighter tori may have to rely more on unbalancing uke and movement.
In my opinion aikido is easier for men, but women tend to have better technique due to the fact that they cant rely on muscle as much. At least, thats from what I have seen.