I had the opportunity to roll through the 2.3 dungeons in an iLevel minimum party to truly see the difference (after weeks of steamrolling them at i100+), and I have to say, they are pretty damn difficult at those levels, and even more so if someone is new. Especially Stone Vigil HM, where we wiped to the triple Aevis room because the healer and monk didn't have enough HP to survive the three AoEs going off at once. It took some planning.

I say the difficulty of 4-man instances is fine where it is.