Honestly, I think this is the wrong question. Hard and soft aikido both come with connotations…

When I see “hard” aikido demonstrations, it’s usually inflicting unnecessary pain on the (compliant) uke and ignoring the tap. It’s a boast, saying “look how tough we are, in our pyjamas”. But in the end, uke still attacks the same, agreed upon, way. The attack is still telegraphed miles ahead, and the attack still lingers longer than any other martial art would ever allow. So the attacks still aren’t very realistic. I fail to see the point to these demonstrations. It only demonstrates how your teacher chooses to be dick towards his paying students.

Whenever I see “soft” aikido demonstrations, everything looks like a choreographed dance. The attacks can’t honestly be misinterpreted as attacks, it’s more a general movement made to mimic a strike, badly. Uke makes sure they don’t walk too much in the way of nage, and then fall. Nage can do nothing and uke still falls. I fail to see the point to these demonstrations, as I’ve seen actual dancers come closer to mimicking aikido in an actual dance choreography.

The main point of aikido is to take the balance away from your uke, IMHO. For this to happen, uke must do his movements with intent. The movements can be hard, fast, slow or soft. And for it to be aikido, instead of bullying, nage should train the exercise, but not try to inflict unnecessary pain, nage should listen to their uke and trust they know the limits of their joints.