Having recently levelled an alt to play with friends I've noticed that it's extremely long and tedious unlocking the level 50 and level 60 roulettes. The major problem is that it requires completion of a significant backlog of dungeon content. I've also found that this appears intimidating for a lot of new players who take several months before slowly unlocking the roulettes.
One simple solution to this problem in my view is to simply shift the roulette entry requirement from "Completion of the following" to "Unlocking the following". This would mean that new players and alts can do the quests to unlock all the dungeons and then simply go through them naturally through roulettes over time.
I also feel it would increase the population of players doing these dungeons as players are just generally more likely to queue into a roulette rather than the dungeon on its own. It would also make going through the dungeons less overwhelming since it would naturally be taken in small chunks.