But there's no reason to run the level 80 roulette anyway.
The total tomes you get from the 80 roulette plus the dungeon, is less than what you get if you just ran one of the two most recent dungeons.

On the subject, I wouldn't be against having a single opt out dungeon, being able to choose just one dungeon you never want to play via a roulette.
I think there's enough competition for 'worst dungeon' that there would still be enough able to run whichever dungeon you need.
Sastasha, Halatali, Toto-rak, Tam Tara, I'd love to exclude all of those, but would be happy getting rid of any single one.