For some games rng can have a place, I'm thinking ftp mmo lockboxes, where players bank on the 0.000001% chance of getting something more than the usual healing potion out of these.
But a vital role in a group should never be reliant on a lucky dip mechanic. To me, this just comes across as a gimmick for gimmicks sake. Any and all classes should rely purely on player skill, not I just happened to get the right card at the right moment in the middle of a hectic boss fight.
More needs to be done with the card draw mechanism. Keep the boon selections but remove the rng. It's an important role - not a lockbox.