Crowley and Shapeshifting
A fair point, he does say he might try the ritual again. But there is the fact that he was unable to take human form because he couldn’t complete it, and we know that we have not seen him in human form since. Where Genn and even his own second in command Tobias Mistmantle take to human form on several occasions, Darius - even when in Stormwind Keep - is only ever in worgen form. He could not shapeshift, he could not complete the ritual, and we have not seen otherwise. One could argue that he simply embraces the worgen curse more than Genn does, but at the same time he refuses to bite Lorna Crowley, even after Sylvanas threatened to turn her into a Forsaken, causing him to retreat from Gilneas.
Theory: Crowley’s “Cured” Blood
Ritual of Balance: Not a Cure
Also regarding the theory of “the cure transfers in blood too”. It is also confirmed the Ritual isn’t a cure, but also that it is not required. We are shown it isn’t a cure, both by the quote “There is no cure, not yet” by Belysra, and by Genn Greymane and his noblemen still hunting wild boar on all fours in Wolfheart. It is said again in Before the Storm that Anduin appreciates the worgen army, since they hunt to eat, and do not need provisions.
Ritual of Balance: Optional
Then we are shown it is not required, especially by the Northrend Wolfcult and the Gilnean Wolf Cult able to shapeshift at will well before the Ritual of Balance arrived. In fact, both worgen cults relied/rely on shapeshifting to find new recruits. Genn Greymane himself is bitten, and maintains human form all through the whole fall of Gilneas, trying and failing the ritual as well but using human form regardless.
Ritual of Balance: Personal
What the Ritual of Balance does do, as seen for Halford and again for Varian Wrynn, is take remind you of your youth, encourage you to forgive the grudges you keep, and shows you have to harness your fury. It is a three part ritual that takes time, is meditative and therapeutic, and is personal. For both Varian and Halford, they still felt the same rage and instincts they did before, but were now in the right mindset on how to use them.
In the end, we have no reason to believe the Ritual of Balance’s effects transfers through the blood. It is neither seen nor stated. The Hillsbrad Refugees turned instantly with no time for such meditation to work on their mind, and act no different than bitten worgen after turning.