Fun vs fair

If the developers feel that balance can not be fun, means something is wrong here.

Balance and fairness are subjective, at least partly. For Fairness, for example, just look at Tunneling. Nobody even agrees on what exactly Tunneling is let alone whether or when Tunneling is "fair".

And for balance, subjectiveness comes in when you decide what metrics you're using to balance things. For example, look at gen speeds. Some people seem to want gens to be completed about 50% of the time and if gens are completed more often than that they're "too fast and not balanced". But if you come at it from the metric of "most games some survivors live and some die" then you have the implication that the Exits will be open most matches which means the gens get done most of the time, not just 50%. So in that metric a 50% gen completion rate would be too slow.

Or another example is which data sets do you use to determine if kill rates are too high or too low? Should you only look at games involving only very highly rated players? Do you use games from the top half of the playerbase? Do you use all games? Or a weighted average of some sort where higher rated players' games count more toward the metric than lower rated ones? How you answer that question determines different results when you calculate your kill rate metric, and you can have things that for instance are very effective against average players looking powerful if you use an All Player filter but looking weak if they're not effective against highly rated players (e.g. Hex: Third Eye Blind has a Semi-Charmed Life against average survivors but does poorly against top tier survivors and survivors on comms.)