My apologies if this has been posted before!
So it was established that Avatar Wan, the first Avatar, merged with Raava and the last Harmonic Convergence was 10,000 years before Korra. When you look at the ages of of the past Avatars when they died, it doesnt seem as if there would actually be that many Avatars in the time between, despite when they show them in the Avatar state communicating. The ages of the last few are below.
Aang - 166
Roku - 70
Kyoshi - 230
Kuruk - 33
Yangchen - 155
Szeto - Unknown
The combined ages come up to 654 between 5 Avatars, but we know Kyoshi was the oldest recorded, Aang bein in ice and Yangchen being somewhat an anomaly. Based of this as its the only data we have I believe, that means on average each Avatar has an average life span of 130.8 years. That means theoretically, only 76 Avatars would have lived. It just doesnt seem like a lot.
I know, I know its just an animation.
So yeah, thats just my thoughts on this delightful Saturday morning!