You already alluded to this in parentheses, but it would completely invalidate the point of the roulette if they did this.
I do agree with the soul of your post though. I'm also sick of being leveled down. At this point, there are certain roulettes that I simply won't do. Leveling is one of them, because the dungeons are largely boring, and the low leveled dungeons are REALLY boring.
It'd be nice to have more roulettes in general. There's a lot of later content that doesn't get any love because nobody runs it. A lazily named "side content roulette" featuring things like variant dungeons, delubrum reginae normal, etc. would be pretty neat. Give people something to do, but on the higher end of the game's content rollouts so the downsync isn't so painful.