A bard that can buff itself, do healing per second on itself, have movement speed weapons, AND do just as much damage per second as a ranging DPS class should be treated the same? The classes aren't meant to have the same capabilities in each situation, or else players would try to find the most "overpowered" class and use that, only. An engineer will now need to either ask for a bard boost, or bring one along, or use all the movement items they can get their hands on. There is nothing stopping you from being an engineer and soloing dungeons!
Short version (tl;dr): Players need to diversify to access all aspects of the game, the bard should not be able to do everything on its own.