It could be that the producers of 24 Oras 2023 had a different vision or casting choices that didn't include Mang Tani. Sometimes these decisions are based on various factors that aren't made public.
Brendan and May in ORAS fanfics are great for exploring different storylines. For example, they could be part of a story where they have to team up to save the Hoenn region from a new threat. The fanfic might focus on how their different personalities, Brendan's more scientific approach and May's intuitive nature, work together to overcome challenges.
In ORAS (Omega Ruby and Alpha Sapphire), Team Magma could be considered a great team for the story. Their goal of expanding the landmass gives a clear and interesting narrative. They are driven by their leader, Maxie, who believes in their cause wholeheartedly, which makes for an engaging story arc as you oppose or side with them throughout the game.
Yes, there are quite a few good Archie ORAS fanfics out there. You can start by looking on popular fanfic platforms like Fanfiction.net or Archive of Our Own. Just search for 'archie oras' and you'll find a variety of stories ranging from adventure - based ones where Archie's character plays a central role in the ORAS (Omega Ruby and Alpha Sapphire) storylines, to more character - study type fanfics that explore his motives and relationships within the Pokemon universe.
Ruby and sapphire are quite different in the ORAS manga. Their appearances, abilities, and the way they interact with other characters all set them apart.
A team that has a clear and unique goal is a key factor. For example, Team Magma wants to expand the landmass. This gives a distinct direction to the story. If a team has a strong leader like Maxie in Team Magma, it helps. A good leader can drive the actions of the team and make the story more engaging. Also, a team that can cause significant changes in the game world, like Team Magma's actions affecting the environment, is important for being the best for the story.
One common theme is friendship. They start as rivals but often develop a strong bond of friendship as they face challenges together. Another theme is growth. Both Brendan and May grow as trainers, learning new strategies and becoming more in tune with their Pokémon.
You can try Fanfiction.net. It has a large collection of fanfics, and if you search for 'archie oras' specifically, you should be able to find some relevant stories.