The Battle of the Heroes in Revenge of the Sith was not the last time Darth Vader and Obi-Wan saw each other, because Vader appeared in the Obi-Wan series.
Obi-Wan Kenobi was more than just a tie-in piece of canon to better connect the prequels and the original trilogy. It's difficult to tackle Obi-Wan's story between Revenge of the Sith and A New Hope, even though that was a time period in the Jedi master's life that live-action Star Wars had yet to explore. Obi-Wan had to create new Star Wars questions and headscratchers in order to tell a compelling story about how he dealt with his failures. Seventeen years after the release of Star Wars: Episode III - Revenge of the Sith, the Star Wars prequel trilogy is perceived in a much better light than it was in the early 2000s. Obi-Wan was always going to either fix or make worse the inconsistencies between the prequels and the original trilogy. In order for Obi-Wan to have any sort of stakes or conflict, he had to hide in Tatooine, which was already a retcon.
The story about Obi-Wan and Darth Vader was re-written at the expense of the Star Wars canon. A lot of things about the original trilogy were explained by the final Obi-Wan and Darth Vader fight.
Obi-Wan Kenobi placed itself in a difficult spot regarding the Star Wars canon by dealing with key Star Wars characters. Even though Obi-Wan was a child when he joined the Jedi order, he still has deep-buried memories of his family, which could be interpreted as a way to explain how Leia could remember her mother. The relationship between Obi-Wan and Anakin was more tragic, and it added an extra layer to the redemption of Darth Vader. To justify Obi-Wan leaving Tatooine, an Obi-Wan show would have to find other antagonists and storylines that justified it.
There are many lines and interactions between Obi-Wan, Darth Vader, and the Skywalker twins in the original trilogy, which makes it hard to make a prequel story. Darth Vader's father, one of the most important moments in pop culture, hadn't been planned out until the final draft of The Empire Strikes Back. In Obi-Wan Kenobi, Leia created a bigger connection with Obi-Wan than she ever did with A New Hope.
Darth Vader and the Inquisitors would be the villains if Obi-Wan was placed on a rescue mission. The Jedi master Obi-Wan Kenobi could not have made a lot of noise because the rebel alliance didn't know he was alive. After Obi-Wan's death, the character never showed any special affection towards him, despite being named after him. Before that, Obi-Wan had created a big discrepancy between himself and his friends. There was a last-minute change to the story that only came to be in Return of the Jedi.
At the end of their fight, Obi-Wan refers to Anakin as "Darth", something he would repeat in A New Hope. During the original trilogy and the prequels, retcons are not exclusive to Obi-Wan. Even if it meant small and significant Star Wars retcon, Obi-Wan was not afraid of taking risks.