Still you see people who already have their pro items devoting all their time on their explorer class, and are still making ultimate adventuers through their Cygnus knight. If you got in game, most of the time you'd still see level 200 explorers roaming around, because they still have interest in their class. Veteran Maplers complain about new jobs when it's mainly for newer players to gain interest in the game. There's a revamp for older classes, but newer classes, are to attract new players and novice alike.
I can also state, new jobs help new players get in the game, and actually learn more. With their damage they would be able to make money, which is kind of hard for old jobs, since merchanting is "hard for them". Nexon can't just break the old jobs and give them overpowered skills, unless they are willing to accept it.