Yeah, but who is?
I'm thinking through the RBs that play for all the top teams and I'm struggling to think of anyone that's genuinely top class. Dani Alves looks great for Barca but would get exposed defensively if he played for us. Maicon is past it. Rafael isn't very good. Sagna is good but not great. Arbeloa again is solid but not spectacular. Azpilicueta has potential but that's all it is right now. Zabaleta at City is a really dependable guy and he's loved over there but often his best qualities are the same ones Kuyt used to get lauded for. And so on, and so on.
If Johnson played for another team he'd probably be much more highly rated. As it happens he gets slated because he looks suspect sometimes in defence (ignoring the many times he gets back to make very timely blocks, interceptions and covering runs). Which other attacking RB doesn't? Johnson is asked to push further forward because he can be dangerous in attack. As a result it's not his fault always that he's caught out of position and it's not his fault always that generally speaking our overrated defence requires a lot of protection to stop leaking goals every game.