I dont have any experiance with MMORPG, only with Fonline. But i think, that there are 2 different ways:
1) You can die very quickly, but also you will be very quickly recovered.. (this is not example of fonline)
2) You are very resistent, so you can fight longer (also this is not example of fonline)
In fonline, you can get 90 dmg in one burst and you are ko if you get 2 or 3 bursts.. So, this is the problem.. Imagine situation, where guns will do 1/3 dmg in compartion to current damages. Fights will be longer then. But you will have to edit hp of critters etc..