Yes you can. Past Avatars decisivly altered the course the world has been taking at the time, Aang and his friends being the best and most recent example. He stopped a war that had been destroying the whole world for a hundred years and afterward he created a new era where people are able to think about stuff like benders having too much power. It's a 'luxury' that wouldn't been there without Aang the Avatar.
Hell, if Aang didn't stop Ozai, the fire nation might rule the majority of the world and a good number of other benders would be imprisoned, with the rest being hunted.
Edit: Just realized I kind of missed your point. Let me work on that for a sec.
You could argue they throw the world out of balance. Yes, in the end it is the Avatars duty to guide the world an make it go into the right direction. But because the Avatar is that powerful, he also changes the 'natural' progression of the world. Who knows what the world might be like without the Avatar. The Fire Nation might rule everyone. There might be not advanced technology like cars which likely were made possible through the exchange of minds from all nations. Its the Avatars doing that creates these things, which can be seen as throwing the world out of balance.
Another example would be Roku's failure with Sozin. His actions, or the actions he didn't take resulted in a war that lasted a whole century, tore the world apart and almost stopped the Avatar cycle. You could say that Roku threw the world out of balance because he didn't live up to his 'responsibility' in stopping the Fire lord.
If you look at it like that, it really isn't normal that one person is granted the power to change the whole world so fundamentally just because he or she was born as the Avatar.
God, I love this show and the universe.
