The purpose of the roulette, as is the purpose of all roulettes, is to get bodies into content that people are queuing for in said roulette. That is it.

The people who are "level scumming" are such an extreme minority of the playerbase it's laughable.
Yeah, I'm sure people are still queueing LotA/ST specifically for the super relevant gear upgrades, or the funsies, or what have you... while people trying to run things like Dun Scaith are waiting forever for their queues. No problem here; definitely isn't because the dungeons are imbalanced or anything!

It isn't as much of a minority as you think.