I don't believe the MCU ruined Tony Stark's character. In fact, it expanded his story and introduced him to many who may not have known about the comics. There were some differences, but they were mostly creative interpretations that added to his appeal.
The MCU timeline would be significantly different. In the early Iron Man movies, Natasha could have been introduced as Tony's sister much earlier. This would have changed the dynamic of his character development. He might not have been as reckless in some situations because he had a sister to think about. Also, in Natasha's storylines, having Tony as a brother could have provided her with more resources and support, changing the way she approaches her missions and relationships with other characters in the MCU.
If Tony Stark were raised by Peggy Carter in fanfiction, it could drastically change the MCU timeline. For starters, Tony's personality might be different. Peggy was a strong - willed and disciplined person. Growing up under her influence, Tony might be more by - the - book and less of a maverick. His approach to technology could also be different. He might focus more on military applications that align with Peggy's values rather than the more commercial and sometimes unethical applications he pursued in the original timeline. Also, his relationship with Howard Stark would be complex. Instead of the distant and often troubled relationship they had, it could be one of mentorship from Peggy's perspective, with Howard having a different role in Tony's life.
Pepper Potts could be a big help. She knows Tony so well, and she could try to jog his memory by showing him things from their past together, like pictures or mementos. Rhodey could also be there for him. He could tell Tony stories about their military days and how they became friends, which might trigger some memories.
One common character paired with him is Bruce Banner. They could be gaming buddies, with Bruce using his scientific knowledge to help Tony improve his games or vice versa. Another is Pepper Potts. She might be shown as someone who tries to get Tony to take a break from his intense gaming sessions.
The character exploration. Arno Stark is a relatively new and interesting character. Fanfics allow us to understand him better, his backstory, his ambitions, etc.
One common character paired with him could be Pepper Potts. Their relationship could be explored in a new light with Tony having psionic powers. Maybe Pepper has to deal with a more powerful and sometimes unpredictable Tony.
It could be Rhodey. As Tony's long - time friend and fellow Avenger, Rhodey would be eager to see him and would likely be among the first to be informed of his return.