We now view this as wrong, but that wasn't beating them.
Yes, some idiots did beat their children, or hit their children out of anger. That doesn't mean it was common.
out of care and love, when they did things dangerous to themselves or others, and sometimes a strap or switch when something truly horrific was done.
In other words, never because fed up / angry. Never because of minor situations, and so on. For example, swearing isn't "dangerous to themselves or others". Spanking employed when the life of the child or others is involved, is a short-cut to locking an intense memory into long-term recall.
This sort of event is rare.
And to be frank? "Improved their lives" isn't necessarily important. Note how I state "dangerous to themselves or others"? Siblings and other children have to be taken into account.
Lastly, and take this from someone with grey hair, it wasn't until my 30s that I started to appreciate some of the discipline I disagreed with as a child. Disagreeing, doesn't mean it was wrong.
We also don't teach our kids to defend themselves against sword attacks, for the same reason - it's no longer necessary.
Your argument implies that the past behavior was bad and we should change it, but that's incorrect. The past behavior was correct for its time. If someone would have raised a child without spanking 100 years ago they would end up with a weak person who could not live in the real world, this would be a bad thing.
In the areas that still do beat their children, they commonly do beat more, when they are angry.