I have eight characters, and of them, four are 50 on a DoW/DoM class, and another is at 47. Honestly, it's not bad at all. Sure, it's more work when you want cross-class skills than leveling everything on a single character, but I find it a lot more fun to switch them up. I think I'd be bored playing ONLY one character all the time no matter what. Running the main story is still pretty quick, so you can get to 50 quite easily without having to worry about nearly as much of the dungeon/fate grind that you hit leveling more classes on the same character. It might be a game that allows for and, to some extent, rewards single-character play, but that doesn't mean it's not fun to have more!