When the US spend trillions of dollars on it's military, is it with the intention to build the army that will deal less damage? Is it with the intention to give a chance to it's enemies? Or is their goal to maximize the effectiveness of the forces? Same can be said about our PvP.
First of all, as you mentioned on Discord, the change will mostly affect OP chars, some of which are nerfed down the line in later patches. It is a radical idea to overhaul the whole PvP system because of 2-3 chars. Especially, if they keep their buffs, debuffs & skills. The easier solution would be to nerf those chars' skills & buffs when it comes to PvP. Leave them as they are for PvE, but limit application of buffs/debuffs & skill % when it comes to PC enemies.
Second, the change will kill all old chars. People should be free to use whoever they like and see fit. Old chars, who are still usable for PvP will suffer a great deal. How are they going to compensate -25%, while they can still be useful at the moment?
Third, there is a reason why people spend thousands of hours farming, grinding, enhancing, enchanting and overall pushing the boundaries of possible - to kill faster & survive longer. There have always been players whos skill is far beyond anyone's reach, whos equipment is in a singular exemplar on the server. They should be able to kill you with ease. It's the whole purpose of endgame, not giving enemies a chance.
Fourth, reducing the damage, but keeping the pots will make no difference. Should you have troubles in killing, people will restore their health in a second and the cycle with resume again. And to counter the point that h0lz brought up about low gear/level players - they won't be able to kill now either. They would have a much lower chance of succeeding at that. Reducing the damage doesn't force you to develop skill. All it does is provides an excuse to those who are not as geared up as others. But then again, how are you going to kill a geared up person with low gear?
Lastly, PvP is not a raid boss scenario and should never be that way. For the purposes that you described there is WxPvP already.
So the bottom line is - nerf those chars for PvP, not PvE, instead of nerfing the whole system.