Dragons, magic and other shit? Fuck yea, no issues there!
There's a big difference,
Having fantasy things, in a fantasy world/setting keeps things within the "logical" for that setting and game.
Either type of game people can get into the worlds because the game abides by certain rules/logic that "fits" within that.
When you create a world and then you have something that takes out the logic or something that seems like it wouldn't "work" within the other parts of the world and setting that you've set up, it can take people out of it.