> I never saw a kid that can't ride this instantly.

As a data point, we tried this with my son, who is physically very capable if not advanced, and despite many attempts over months, it never clicked for him. We eventually went the training wheels route, which he instantly adopted, and once he was comfortable on that for a while, he learned to ride without them in a single session.

We've since met other parents who had similar experiences, so I think it's definitely not a universal thing that balance bikes are better or even useful.