I agree that raid bosses should be challange. It should be hard but possible.
Maybe I am wrong, but I cant see T1 bosses to be any harder. Only thing that make them harder was gem nerf and of course bugs (but I dont count them).
I dont know about T2 bosses, but there were very easy before patch and you can kill them without full raid and without T1 equip pretty easily.
Kilikky
pre-patch: The easiest boss from T1. Even if she require some tactic, it can be done with good PUG.
after-patch: I think tactic and behavior is almost the same, but its not the easiest boss now.
Yakhmar
pre-patch: The hardest to kill from all the T1 bosses. It was especially its minions what makes this boss difficult. Onther than that he is very dull.
after-patch: Minions was nerfed so he now take position of the easiest boss of them all. It requires no tactic and any PUG can do it. Its probably also bugs, but its not that obvious
Vistrix
pre-patch: He was like example of good T1 boss. Maybe it could be just a little harder. But it require good team, coordination of banes, good timing. Quite hard with PUG, but for premade raid teams piece of cake.
after-patch: He didnt change that much. There is more fire breaths but nothing radical. What is the most important after patch are bugs!
One that remain from past is path finding bug and the second (new one) is reseting to full health. Its important to prevent exploits, but this is too much, he resets almost every time he kill someone.
Just my oppinon.