Probably not materially faster than they leave - over the long run.

This first graph is mostly dominated by mastodon obviously we don't know who did or did not use reddit previously, but its a general pattern.
https://fediverse.observer/stats&months=96

Similar pattern in monthly active users for lemmy specifically.
https://lemmy.fediverse.observer/stats&months=96

I don't know about newer versions like pieface or whatever - but since the total fedi population is fairly stable any specific software is probably mostly shuffling the same people around.

Though maybe the dataset doesn't crawl stats for newer ones, I don't really know - but it feels pretty stable population with inflows and outflows more or less matching.