They swapped up DH a bit here. You no longer get value from using Blade Dance as a part of your ST rotation unless you purposefully don’t choose Glaive Tempest which will cripple your overall damage.
As someone who plays both specs, Vengeance is actually in a good spot at the moment! I knock out so many orbs while dungeoning it pays off. You’re right in that my initial mythic dungeon attempts were made a bit harder because of survivability (even ensuring my defensives were up) but they quickly became do-able. It’ll be even easier as we gear into Heroic-level gear and upwards.