It’s mostly a feeling and could be wrong. It’s fair to doubt too since they have completely different attitudes in the scenes we’ve seen so far.
When Cliff was first introduced I immediately thought there where similarities to their appearances. Though Cliff seems much more kind and caring towards Leon a change in attitude could easily be explained through some yet unseen character development or by some misunderstanding between the two. For example if Cliff feels deeply betrayed by Leon for some reason that could have changed his behaviour.
Am I the only one thinking that Nargal and Cliff are the same person?
The markings on Cliff’s face seem like a charm restricting his abilities. I think It would explain Nargal’s attachment and possesivness over Leon perfectly If that where the case.