Then I guess reality is unrealistic. Just look at technological progression in real life.
It's not even a real complaint of mine, I just thought things would be more believable at 150 years. The time from early locomotives (1820s) to automobiles similar to those shown in the first episode of Korra (1920s) was around 100 years, at least. It's definitely believable of course, but a bit jarring, especially when they could have set it later and it wouldn't have raised any flags.