I would just ban top rope headbutt type moves period, slap or no slap. As you said it looks atrocious 90% of the time, if you fuck it up you give each other severe head trauma. There's no upside here.
Funny how as a kid I never noticed the bias since I too felt NWA/WCW was better. It is pretty apparent looking back, but at the time I was like "yeah this all checks out". It wasn't until 97-98 that I thought the WWF was the better product.