Also since Luna joined the crew he almost died 2 TIMES if not for her saving him. And I'm supposed to believe that this guy somehow built this criminal syndicate without dying much earlier? He really does feel like a filler antagonist that a much more imposing motherfucker is going to replace later (except it wont happen)

Vargas didn't build the syndicate though, he's a sub boss. The 2 times you are talking about also didn't happen, the first one in episode two is stated that he was going to kill the guy shooting at him, it was just Luna being worried about the situation.
Aiden and Luna reactions when they see that Vargas fights using a knife against people with guns, say a lot about how strong he is. The only thing worth talking about is the second time you mentioned, but the guy he was fighting with (can't remember the name) is described as insanely strong, so it makes sense he might be stronger than Vargas.
I actually liked seeing that scene where he was having some difficulty instead of being a godly creature impossible to beat.