Def and VIT are not broken. They reduce damage by a quite significant amount compared to someone taking hits with their face. Anyone remember the old Dynamis when DDs would get one-shotted by Eagle Eye Shot even from *non* NMs (which would do 500 or less to a PLD)? There's nothing preventing current NMs from having equally dangerous attacks, except the devs chose not to give them any. But then the DDs would just all sub NIN...
Reducing damage by 100% with a 100% proc rate (which is what utsusemi is until the shadows run out) is broken. SE refuses to nerf it, therefore, nothing else they do will fix the real problem, unless they give every NM Hundred Fists, which would be kind of boring.
Players can keep throwing out suggestions (I kind of like the idea of having a check each swing based on mob level vs. ninjutsu skill for the mob to "see through" Utsusemi and hit the player, which would appropriately nerf /NINs and put them at some real risk when they take hate without having too drastic an effect on main NINs) but if SE continues to allow 100% damage reduction with a 100% proc rate, no other method of mitigation is going to be able to equal, let alone surpass it. Utsusemi effectively already *is* permanent Invincible -- except better, because it also works on single-target magic damage.
Ochain: large percentage of damage reduction, but less than 100%; high proc rate, but less than 100%.
Utsusemi: 100% damage reduction, 100% proc rate.
...a level 37 subbable spell is more powerful at avoiding damage than a damn empyreal and we're arguing about what JAs could be adjusted?
P.S. Part of this has to do with haste proliferation making recast timers a joke, but I assume SE isn't going to nerf Haste either, even though they definitely should. It's an unbalanced uber-stat for DDs and god mode for Utsusemi/DD tanks.