A simple redesign of how A and S rank hunts should be easy enough to achieve. Increasing their HP by a scaling factor that is based on number of people near the mob is a great idea. This makes the fights longer (allowing more people to get there in time) and also makes it more interesting.

I am on Sargatanas and most A ranks die within 10 seconds. S ranks are around 30 seconds. This is not much of a window to get there. Sargatannas also has one very notorious early puller whose name I cannot mention due to forum rules. I can; however, say that his name was inspired by the dragon ball z series

This behavior has actually led to many of the tanks in the community resetting mobs when that particular guy is involved. Steal aggro, pull away from spawn location, reset for the win.