If you are hand-managing VPCs then there is every chance that this additional layer of complexity will lead to mistakes. You could argue that the increase in cognitive load of managing them can offset the benefits of an additional defense-in-depth control. New developers joining the team are likely to make mistakes and this is the sort of thing that doesn't get caught in code reviews either.

However, VPC configurations are an essential defense-in-depth that can be programmatically managed. AWS-managed VPCs are certainly not hand managed.

While maintaining Cloudformation or Terraform templates is still a pain, the good news is that it is becoming increasingly easier via frameworks like AWS CDK. This allows your deployment code to programatically generate the infrastructure and VPC configuration. This decreases the likelihood of mistakes made in configuration and increases the chances of such mistakes being caught during code reviews.