This is my simple view: "hard" aikido means a committed, real attack, waza which neutralizes the attack, and a finish which employs absolute focus, kime. It is my view that only hard throws/locks/pins can ultimately press one as uke to learn the paradox of a complete attack, coupled with the ability to hungrily sieze on nage's body/mind, so that whatever changes nage executes I can execute, instantaneously, without hesitation of body or mind (going back to my earlier thought re: getting out of the way), and without reserve, to take the fall, lock, or pin. And this ultimately gives me the sensitivity and ability to train, as O'Sensei urged, with a "fierce joy." Both fierce, and joyful.
As nage, my job is to lead uke to where I want them in order to effectively execute.
It is not to create a "harmony" where uke and nage are in essence, in complete agreement..."harmony" can be anything, almost. To illustrate bluntly: if someone wants to shoot me, I can "harmonize" by allowing it. Or I can kill the attacker with a break to their vocal chords/trachea. Or I can disarm the attacker by leading them into my orbit of control. All are versions of "harmony." Aikido teaches the latter, but I think it is often misunderstood to mean, as I earlier said, a type of dance where nage/uke, in seeking to build grace, do not really require much from each other. I don't find this useful.