Nah I disagree with that. Rambo 5 is easily the worst Rambo movie, and it's true that the story is a generic revenge story. But, he still felt like Rambo to me even without the hair and the headband. He talks more. That's because he's spent the last decade at his home, with people who have actually become his family.
The bit where he easily gets followed by the cartel was stupid, but apart from that he still acted in character and was badass the whole way. Even in just small moments like when he threatened the girls father or her friend who screwed her over, he was still extremely intimidating and even downright scary.
The final act is easily the best part of the movie and harkens back to all the traps in First Blood. I'm a huge Rambo fan... was 4 a better ending? Yeah. Am I also happy to have one more movie with him after that? Yeah. It's an enjoyable movie, With a badass Stallone performance, and seeing Rambo at a different time in his life was cool. It isn't a disgrace to the franchise like "A good day to Die Hard" was to Die Hard.