Yeah, I also experience this quite often. And it's just weird. I don't mind doing Sastasha or even Toto-rak (don't understand people's issues with that place tbh o.o) when there is even just one person in the party who's of the appropriate level (and potentially doing it for the story). But when everyone's 10-20-30 levels above and is only there to actually level their Nth job? I don't see why the roulette couldn't prioritise a dungeon that's actually closest to whatever the lowest level in the party happens to be.