Personally, I feel like you can't tell a decent story for scifi or fantasy in less than 10 episodes. Amazon and Netflix seem to be hovering around 8 episodes as their preferred season limit. It isn't enough, I think. WoT had a decent budget, but that story felt really rushed in season 1. The Expanse was good until the final season, rushed again.
The Witcher season 1 was 8 episodes but I feel like they went for the 1 monster per episode format with only minor scenes for the overarching story, it worked. Season 2 did not work as well for me. The Mandalorian did the same thing. Season 1 was 1 mission per episode while building the arc for Baby Yoda, I liked it. Season 2 felt rushed because they focused on that story and there wasn't enough with 8 episodes.
Maybe it's just me, but 8 episodes doesn't seem to work if you want an epic storyline told.