But was the old way really that ineffective? I remember driving to a big empty parking space on a Sunday with my father, he removed the training wheels, and after around 30 minutes, I got it. Learning to ride a bike isn't complicated, what makes it look so hard is that it is a sort-of binary skill. You can either hold your balance, our you can't, and so it will look completely impossible until you suddenly can do it.
Tom Scott learned to ride a bike in this 30ies, it didn't take long [0].
Interestingly, "training wheels" aren't called "training" wheels in Germany, but "supporting wheels" (Stützräder), and when I was a kid, nobody used them to "train" their children to ride a bike. They were used to transform the bike into another kind of vehicle the kid could use until it was old enough to learn to ride a bike.