In most cases, playing as undead John Marston isn't a feature in the story. The game developers likely had other creative directions for the gameplay and narrative.
The duration of John Marston's story in RDR2 depends on how you play. On average, it can take several dozen hours to complete his main storyline and related side quests.
William Moulton Marston was a multi - faceted individual. As a psychologist, he was intrigued by the human psyche. His idea for Wonder Woman was a blend of his psychological insights and his view on gender roles. He wanted to create a character that would break the traditional mold of female characters in comics. He was influenced by the women in his life, including his wife and his mistress. His vision for Wonder Woman was that of a strong, intelligent, and compassionate woman who could fight for justice. This led to the birth of one of the most iconic superheroes in history.
It can be considered a true story to some extent. The film takes elements from Marston's life and presents them in a fictionalized way, but it retains the core essence of his experiences.
I'm not sure specifically which 'Jack Marston Christmas Story' you are referring to. There could be many fictional stories about a character named Jack Marston during Christmas. It might be a story created by an individual writer, in which case more context would be needed to accurately tell the story.
One reason is the character of Jack Marston himself. He's a complex character from the game, and fans love to explore his backstory and potential futures in fanfic. His growth and journey in the original story leave a lot of room for creative interpretation.
One possible theme could be redemption. Maybe Jack Marston has made some mistakes in the past and during the Christmas story, he tries to make amends. Another theme could be family. If he has a family, the story might focus on their togetherness during the Christmas season.