WhatsApp's unusual badge behaviour is quite good for most people (not tech savvy, completionist, or OCD).
I've you've ever looked at a normal person's homescreen I'm sure you remember how you felt as you gazed upon their 5-digit red app badges. Gmail 31,415. Messenger 652. YouTube 927. These are meaningless and to them impossible to maintain. They cope via Notification Center, where their inaction is equivalent to us clearing.