Role-playing games are a subset of games. For the purposes of this discussion we are assuming some variant of Dungeons & Dragons. What is important is that it comes in a book with rules which is enough for us to consider it a game instead of play.
One thing that marks Role-Playing Games as different than more straightforward games is that the constraints are fluid. I know this sounds like tedium obviousness 101.
In a recent discussion Noism's of Monsters and Manuals stated:
"Different people have different tastes and different groups of people respond in different ways, there are good general rules of thumb that work universally."
That's the baseline for our conversation. If you're wrapped up in the idea that something being objective makes a statement about your personal value or worth, then you have self-esteem issues.
"He's examining and evaluating something I like! Because I have poor esteem and boundries I think that must mean he's evaluating the core of who I am as a person! I had better go to war to defend myself to let everyone know that what I like is immune to categorization and then I can continue to go around and be in denial that in one hundred years after my death no one will ever remember who I am." - The Internet
Playing to Win?
Spike, Timmy, and Johnny)
So, rather then just a well-designed game with a victory state, there are choices that still appeal even though they are less effective at achieving that victory state.
There is no situation in Chess where I would refuse to move a piece that would allow me to win, based on my opinion of the piece. Successful tournament players in Magic also don't use cards that don't help them win. That is the metric for card selection in tournaments "What card will help me win?", It is important to note that not every game of magic is a tournament game.
Taste is irrelevant when the only goal is achieving victory conditions.
Role Playing Game Balance?
However Dungeons & Dragons is different because it pushes the importance down on those 'win conditions' because play still continues (a 'la Zak's infamous "Dying prevents you from playing the game a certain way.") It also ups the importance of the sub-goals: Exploration, Problem-solving, Drama/Acting*
What this means is that rule changes and systems in Dungeons & Dragons can be objectively comparatively judged based on how well they meet these design metrics.
That is to say that decisions about the value or use of systems can be made without being influenced by personal feelings or opinions.
That is what objective design means. "Do you want to use it?" is surely subjective, but as to how it affects the game? That's a matter of objective design.
*understand that "Drama" does not necessarily mean anything in play, it can also be about the structure of play leading to this upon reflection. There is an implicit 4th category, "Power-gaming" which is solely focused on achieving the win conditions.