Some lvl 50 or below duns can be challenging than those lvl 60. You have a point, but I think it would be alright if those new duns became easier to handle after some time, especially with higher ilvl gear. If these duns became harder in any way, it would be troublesome while taking a grind - expert roulettes for example. Among all the dungeons I play with lvling roulettle, I become concerned when AV or the vault pops. Personally I don't have any problems with those two except the fact that many parties end up undersized or abandoned.