Been away for awhile. I agree one needs to hit something or it's easy to get in the habit of "arm punching." Also there is feedback from the bag or training partner.
I don't use a Makiwara, but can see its benefits. It's only a pushing strike if ones lower body isn't linked to the core and torso. If done correctly Makiwara training helps link the body as a whole for striking. This would be for a self-defense scenario. In sport karate this linking isn't a focus.