I addressed all that. Requiring people to have all available duties unlocked before granting them roulette access would increase the number of people available for more duties instead of allowing people to focus their roulettes on a small number of duties.
They can avoid the duty by not running their roulette today or leaving the duty if their roulette puts them in it.Personally, I wouldn't want someone who had a bad experience in any content to be forced to do it again before they are ready to retry it. Because they aren't in the right mind state that they can do it. They'll be more likely to mentally check out the first time they mess up a mechanic or the group messes up and wipes. I'd rather they try it again when they are ready.