Reva's story was needed in this show because without it, there is zero tension in terms of what will happen because we know exactly what happens with all the main characters. We know that Leia will be safe, Kenobi will end up back on Tantooine watching over Owen, Beru, and Luke, Vader isn't getting killed, etc., but we really didn't know what would happen with Reva. We all predicted it but the show didn't even confirm her backstory or true motivation until the last episode. So her story did bring a bit of tension into this.

That being said, it speaks to the greater issue of "should this even be a show"...there really isn't a compelling reason for this to exist other than it's cool to see Ewan and Hayden back playing these characters. In universe, there's nothing ground breaking here. We know how this story goes. It's not like Rogue One for example (my FAVORITE Disney/Star Wars thing, and maybe just maybe my favorite Star Wars movie of any kind). In Rogue One it was also a "prequel", but there was a complete cast of new characters who all have decent arcs in one film, and we didn't know how it would end for any of them. Even with having them all die before the end, each character got their own meaningful death scene instead of all of them just dying from the Death Star attack. So THAT was an "in between" bridge type of story that worked and completely justified itself. Kenobi was a good story, but eh...