> Why would it shorten the growth period compared to mainstream platforms, where there are far more users who could join the community?
Because networks tend to follow an exponential growth rate.
The time it takes to go from 1 to 128 equals the same time it takes to go from 128 to 16384, so if you add 127, you've shortened the time for the network to grow from 1 to 16384 by half. Meanwhile, for a platform that already had 16384, subtracting 127 is a drop in the bucket.
> Is there any evidence that this is the case?
Facebook/Youtube/Twitter/et al couldn't have grown as much as they did as fast as they did unless that was the case.