I didn't have a problem with Hayden because I think he's a good actor in other movies. The dialogue and how it was delivered was all Lucas' fault for not directing him. I think Hayden should just always open with "Hey me and the Prequels weren't the worst thing to happen to SW after all, huh?"
Even if it's a 10 year old in back ground shots that never has any real dialog - you still have to cast them. It'd be one thing if he's routinely meeting ben in secret for secret training, but we know that's not going to happen.
I'm guessing the young Luke will either be utilized in one of the following ways. In the old EU books, they mentioned Obi-Wan running into Owen and Luke while they were in town shopping and Owen chased Obi-Wan off. The second would be a scene or scenes where Obi-Wan approaches Owen to train Luke, which is mentioned in SW. The last would just be a far off shot of Obi-Wan watching over him from a distance. If they doing anything besides those, it won't work and would be contradictory to the dialogue in SW where Luke doesn't really know Obi-Wan, he just a weird hermit.
My point was that this show and any other Star Wars content involving known characters is only going to erode the existing stories because in order to have interesting material to work with you have to often break the canon established in those existing works. Which is why I've argued for years now that it's time to move on from known characters and scenarios and the sole reason why the first season of The Mandalorion was so successful. That show was a hit because it dared to do something new. At least until season 2. Then it took a nose dive into the familiar.
I love Ewan as Obi-Wan but unless they handle it with care (and history has proven they won't *cue Geode) then it will change the continuity of not only the OT, but the PT, Clone Wars and Rebels. So for those who are quick to dismiss this as whining, just don't be shocked when you see major continuity problems come up as a result of the writing.
I hope I'm wrong because the idea of Ewan reprising the role does sound appealing in theory but I've long given up hope on this franchise. It's the proverbial scab fans can't stop picking. Don't be mad when you're left with a scar.