lol @ Street Fighter being balanced Yun and Yang were intentionally made to be overpowered as stated by Ono.
That being said, it's not as unbalanced like the likes of Ultimate Marvel vs Randomness:Fate of two Scrubs.
What makes a good fighting game is all of this
-Accurate Frame Data and Details in Fighting designs and mechanics. Every move should have specific data and be somewhat detailed. The fighting needs to be robust, mobile and have mechanics that add to the gameplay without detracting from a show of player skill/ actual gameplay.
-Balance. It's impossible for every character be on equal footing as one another. However balance lies in the fact that every character should be able to have an answer for their opponent and vice-versa. On a grander scale, balance allows two opponents to test their skills on equal footing. Balance is usually represented by a Tier list, however a tier list is examplified by Balance by how small or large the GAP in the tier lists are. For example, in a game like Marvel vs Capcom, the gap within the tiers are extremely large with someone like Vergil being on a completely different level than someone like Arthur (being one of the worst characters in the game).
Responsive button inputs and Robust Innovative Mechanics. A Fighter needs responsive button inputs so that a player can 100% of the time input whateverso he chooses in any given situation.A combo system isn't always necessary (Street Fighter didn't have one originally), however that didn't mean it didn't have responsive button inputs. Responsive Button Inputs allow a Player full reign over his/her character and allows that to use said character to their best potential. Responsive Button inputs also can evolve into allowing combos, which falls under a robust mechanic. A Fighter must have stable mechanics which equalize the gameplay for all those involved without loosing the intrest of players.
-Interesting Characters who are different from one another. A Fighter needs different characters to garner intrests of said player and allow said player to play whoever matches his playstyle. It offers individuality and leads to more diversity within the game. A game without interesting characters will not survive. Within said interesting characters must lie different movesets for each and different individual moves for them as well.
A tier list is a theoretical list that ranks each characters matchups and strengths against others when both are played at full potential by two equal players. Usually a tier list shows which character has the best matchups, and which character has the worst.