Not really. There've been plenty of movies that are older, have had no follow up material and have had a much larger impact than Avatar did.
Plenty of films that have had sequels that still would have had a much larger impact than Avatar even without the sequels too.
Exactly. RoboCop, Predator, Alien, and Terminator are good examples. In the Alien and Terminator's case, they definitely blew up larger with the sequel, but they were already popular before it released and already made an impact on culture. Especially Arnold and his "I'll be back." Most kids couldn't even watch those films, yet they knew the characters and lines from the film, as well as bought the toys and dressed up as them for Halloween.
It's got to be almost a decade since I've seen someone have an Avatar toy or dress up as a Navi for Halloween. Haven't heard a single person reference a line from it or even know the name of one of the characters, even if they claimed to like it. No impact whatsoever. The only people who reference that movie without being provoked to either talk about how forgettable it was or how much it made. Yet, somehow, Cameron thinks Avatar sequels are his future. And this is really why it's taken him this long. He has no idea where to go with the story or is searching for some other gimmick to turn a mediocre film into a huge success.