I'm not sure what you're trying to say here. Are you suggesting that we should excuse parental abuse, because a child would be a worse parent than an adult?

not at all. Some people are objectively bad parents.

I'm just that in general, the heuristic is accurate that parents have better decision making than their children. The very real counter examples (eg abuse) don't negate the trend.

And somehow also strangely arguing that most parents are abusive?

Not the best phrasing on my part. Better phrasing would be "consider how likely the average parent is to be abusive"

That said, all parents make bad decisions to the detriment of their children. The severity and frequency is what constitutes abuse vs mistakes.