The evidence is 100% certain that if you hit a child, you're increasing the likelihood that they will have poor outcomes. That includes mental health and physical health. It also includes across the other domains of development—education, justice, etc.
Does that mean every child who is hit will have these outcomes? No. Some children will be more resilient, and we're learning about why that's the case, but with 100% certainty, there's no question with the decades of data and thousands of studies that if a child is hit, spanked, slapped, whatever word we use, you're increasing the likelihood of poor outcomes for that child. That child will be less likely to reach their full potential and less likely to be in optimal health. That's 100% certainty.
Importantly, there are no studies, not one study, that show that hitting a child is beneficial to the child.