You can assign a Devotion skill to any of the Dual Blades skills but those skills have only 20% chance to be used. So for example, Dryad’s Blessing has only 6.6% chance to be procced (33%*20%). We don’t have enougth skills to assign Devotion Constellations to when playing Nightblade. Other skills have long cooldowns. I can assign Living Shadow to Shadow Strike that is ok but the rest… Assassin’s Mark, Dryad’s Bleessing can only be assigned to the Dual Blade tree skills and that causes that issue I told about. It just not fair that we have to rely on 6% proc chance instead of 33%.
It is actually VASTLY more favorable to DW nightblade than you make it out to be. First off your best proc can go onto your attack replacer (b. fury, Troll Rage, Firestrike, etc) and then you can assign the others to your various DW weapon pool skills. Keep in mind that each of those skills hits at least twice when they go off and you can trigger two devotion abilities at once thanks to your ability to use the WPS with an attack replacer.
Also nothing is stopping you from picking up blade spirit or some other pseudo-pet depending on 2nd mastery to trigger effects.
How that changes the fact that we have only 6% chance to proc Dryad’s Blessing , for example, instead of 33%? with on crit skillls it is even worse. You have to crit (and you usually have only 10-15% chance on bosses) then you have to coincide that crit with the skill devotion was assigned to. That makes only 2-3% chance to proc on bosses and 4-5% on other monsters. Not fair imho.
Again, you are vastly over-stating how hard it is to proc things with DW. Lets say you stick Dryad’s Blessing onto Quick-Cut. It is fairly easy at 20% chance to trigger on average about 2 quick cuts every 3 seconds - at 3 attacks each. Given that each of those 3 attacks will have a 33% chance to trigger the heal, and the heal has a 4 second cooldown you’ll still be looking at the cooldown controlling frequency more than proc chance.
I mean most DWers use Swords or Axes that I’ve seen, so you’ve got fast attacks going for you, ALL of the dual blades line skills hit two-three times per triggering (and two of em in an AoE!) And you can still put your favorite onto an attack replacer and it’ll trigger constantly. There is zero problem using devotion with the DW line - I’d even go so far as to say it is one of the builds that can utilize multiple devotion procs easiest. (others being totem druids and pet mancers)
What Silben said in the last post is spot on, I am running Dryad on my newest blademaster and I proc it on cooldown or close to it. On crit devotions not bound to your attack attack may not proc a ton if you’re not a blademaster with fa oa, but hey no one says you have to use them 
I don’t think they’re particularly good if you’re not nightblade + not soldier either and not just because you can’t proc them super often