Girona have been great in the last two seasons. But when it comes to trophies I agree with what you have said that it is still quite difficult for Girona. What differentiates Girona from Madrid or Barca is that both teams have quite good squad depth. Playing a fairly busy match between La Liga and the Champions League certainly requires consistency in the game. And if the reserve players are not as good as the main players, it will be a problem if some of the main players are injured. So apart from good performance, consistency is also needed to become a champion.
Girona's quality may only be good for La Liga and to measure how well they can manage their busy competition schedule they will have to try to get a place in the champions league next season. I agree that every team must have reserve players who are as good as the main players and that is what Real Madrid and Barcelona currently have, so however, Girona, with the depth of their current squad, I don't think can match these two teams in the title race. Being able to finish in the top 4 is a very realistic thing for them.