Complaining about adjustable difficulty is like complaining about memory saves instead of passwords or maybe saves in general. It's not the game dev's job to guess how capable you are, if you misestimate yourself you should be able to correct it without having to play through the early parts of the game again. If you don't want to use the option don't use it, I've played plenty of games where I could have adjusted the difficulty in midgame but didn't. Takes much less restraint than, say, voluntarily limiting your credits in an arcade port.
RPGs can be a mess, but the balance issues are inseparable from the gameplay. If you take out character development, it's hardly an RPG anymore. If you make sure the game is always challenging, then every player, no matter how good, will have to level grind (ala the original Final Fantasy and Dragon Quest games), although these days that sort of RPG is considered classic by many people. The other side of the coin is to make sure the character is overpowered and then many people will find the game too easy. Finally, some developers give you the illusion of character development, so that they can be certain of maintaining the challenge. That's probably the best way for the most people, but there's still some that prefer the old-school method of course.
That's missing the RP in RPG. There is no reason an RPG needs character development in the "god" direction, there is no reason a late-game character needs to be able to withstand fifteen shots in the face. You could have an RPG where the player remains at a constant strength throughout, the development people want to see is of the character's character, not his physical traits.