I don’t think you can look at a few successes and conclude that accents aren’t an impediment.
All you’ve shown is that accents aren’t a dealbreaker. Movies with British accents can be successful in the US. Showing that being full of accents isn’t an impediment is much harder, and I’d be surprised if it’s true. The fact that American remakes of British films/shows tend to be more successful than the original (in the American market) suggests that accents are an impediment. Of course, it’s all mixed in with stars, cultural differences, and the many other things we’ve listed in this thread. It would require some careful statistical analysis to pull out the actual effect of British accents on the American market. We can’t get there just by giving examples on either side.