While I'm not entirely opposed to mobs interfering in combat, I think it's important to remember that generally people who want to PvP want to test their skill and ability against someone else directly. While it can be argued that mobs add a layer of complexity to the fight, they still represent something that is out of the player's control that has the potential to completely change the outcome of a fight. I don't PvP very often so please correct me if I'm wrong, but in general people PvP for two reasons:
- Because it's fun.
- Because they want to directly compare their ability to their opponent's ability.
Sure there is an argument that mobs add an additional layer to PvP, but is that necessarily a good thing? Obviously a large amount of PvPers are having less fun and not enjoying the experience because they have to spend more time concentration on the AI than they do their opponent. It makes the experience less enjoyable. There is a reason that every time we have 1v1s or mock team fights in our town dark room we turn on the lights and clear out the mobs first. As soon as mobs get involved instantly most players are having a less enjoyable PvP experience. I would also like to add that I can't recall anytime we've had someone get killed by a custom mob in our town fights and not complain that it wasn't fair because the mob interfered.
On to the second reason, as soon as an AI is introduced a players skill is no longer compared solely to their opponent. The custom mobs change the dynamic of a fight from a 1v1 to a 1 vs 1 vs mob. When you lose a duel to someone generally you can break down the fight and figure out why you lost and how to improve. You can find your weaknesses and work on fixing them. When two wizards are dueling and one of them gets hit by witherfire for 33% of their health it's a lot harder to determine where you are going wrong. You have to wonder if you were actually going to win the fight you just made the mistake of being two blocks closer to the boss mob than your opponent, or if you were generally outplayed.
So what is the solution? Honestly I have no idea. I personally enjoy the custom mobs for PvE and leveling, and I enjoy that the nights actually feel dangerous again. That being said, there needs to be a way for players, large groups especially, to PvP without needing to worry about the mobs. I really like the suggestion of making the mobs not aggro during the day because there is no reason the world has to feel so deadly 24/7. Minecraft has always been about exploring and building while the sun is up, and hiding or hunting when the monsters come out at night. At least with this solution there are still mobs to level with during the day but the environment won't feel as oppressive, at least not while the sun is still out.