The New York Times ran a piece by Evelyn McDonell, the former Village Voice music editor who worked with Jonathan Larson on a book about the creation of Rent. It replays an inteview she did with Stephen Sondheim, not long after Larson's death but after Rent had become a hit, about that musical, Larson's previous works and Sondhiem's relationship with him.
I'll let people with more expertise on Sondheim and Larson opine, but McDonnell's article and Sondheim's candid remarks are interesting:
https://www.nytimes.com/2021/12/13/movies/stephen-sondheim-jonathan-larson.html