I feel that leon becoming a government agent along with sherry made him more relevant to storyline, especially since us made dealings with umbrella and the family was the main reason for the country's corruption. Since re6 delves into this the most, ı find leon's utilization the best there along with other returning characters. I wished they delved into government corruption plot much more but vendetta keeps important story info in the novel while infinite darkness is set in the past. Wonder how death island will turn out.Personally, I have no issue with Leon. Others may feel he is overrated. I think I like Chris just a bit more because he was there since day one.
However, Leon is great in the action games too, and the movies, and because of his role as an agent, he gets the international adventures. I also really like Chris and his, "I am tired of this shit taken away the ones I care about" approach.
But his RE7 model is horrible. His RE8 redesign is not bad, but I think he is gonna retire soon. Unless all the games he will be in will be prequels to the DLC, as it does proceed quite far into the future, with Chris announced to still be alive.
One downside to using fan favourites though is that it can take away from the horror feel. If they are used to it, as you the player is, you cannot be creeped out.