I think a better way to counter this would be a more reactive reward system for dungeons. To a limit based on how easy a dungeon is (both skill-wise and time-wise), rewards for dungeons should increase when fewer people are playing them, and vice versa. This way people are encouraged to get involved in other dungeons even when they aren't using Duty Roulette, and also if people are clearly spamming a certain dungeon then the SOL/POE reward would slowly drop as a means to encourage them to try something new.

But then, I rarely go into dungeons because I find dungeons annoying by default, so my opinion isn't worth a huge amount. xD