Like Mellaus says, T3.5 isn't harder than some of the T4 fights, it's just that more people are used to farming the T4 fights so they know them better.
I can honestly say that the Bat is the only raid boss left in the game that I still enjoy doing every week. So I would be against any nerfing.
We all know that the easiest way to make an instance popular is splashing some new loot on it, but you also want to avoid the irreversible loot escalation problem.
I was happy to see some new loot distributed in T3.5, but even I would agree that the drop rate is a little too low.
The next issue is this contrast between people complaining that instances are too hard - and people who don't want them to get any easier as it will ruin the challenge.
Funcom's solution of bringing out Normal and Unchained instances to cater for different levels of players, seems like a logical one.
I wouldn't be against implementing this on T3.5. For example, the Normal Mode gets nerfed but only the old loot drops - whereas the Unchained Mode stays at the same difficulty but you increase the drop rate of the new loot.
I don't like seeing players in the game saying "Oh, I wish I could see the Bat fight or Lurker fight just once". These are good, fun fights and ethically, everyone should be able to enjoy the experience.
Jonny.