These numbers suggest very little sustained loss in traffic

You'll probably see a decent sized dip at the point where the changes go into effect. There are probably a lot of people using apps like Apollo until they can't: once they can't, certainly not everyone is just going to go install the inferior reddit app and start using it.

Also, it's possible the relatively small drop will have more of an effect than might immediately be obvious. Social media sites like reddit, Twitter, etc aren't really that profitable (when they're profitable at all) — but people are willing to invest in them because they're currently still experiencing growth. So in this case, growth has not only stopped, but reddit lost some ground.