This only happens if the alternatives offer better rewards. People left Steps of Faith because they knew they could queue for Trial again and likely get something else. With Expert Roulette, your choices are limited to whatever the current new dungeons are. Look at Weeping City. Despite all the initial whining, people eventually sucked it up because if you wanted to upgrade your Lore gear or get gear itself, you had no choice but to learn and embrace its challenge. And WC isn't even "hard". It simply keeps you alert due to the sheer amount of mechanics-- none of which are overly difficult once you figure out the pattern. If dungeons followed a similar design, I think people would gradually adapt.
If you maintain the status quo, what motivation do people have to improve? The lack of any meaningful challenge is why people 1-2-3 combo. They know they can get away with little to no effort and get carried. If dungeons were made so DPS who didn't do an active rotation became slow, sluggish or even dangerous, you would gradually see less "Ice Mages" either from community demands or those players getting frustrated the rest of us can't carry them through. Right now, I know I could Impulse Drive the whole way through Hullbreaker Hard. I'd be bored to tears, but I could do it.