In foreign-language congregations (which make up more than 25% of the US congregations): there is still lots of growth--especially among poor and/or semi-literate immigrants. The appeal of people who are well-established in this country, offering them literature in their own language, and later on a foothold of stability (belonging to a well-estblished "church"), is quite strong. In some immigrant-heavy urban areas, it is not unusual for a pioneer to be conducting 10 or 12 studies simultaneously, and have 2 or 3 of them progress to baptism every year or so. Very very few Latino immigrants, who grew up in hovels very likely with dirt floors and no running water before spending their life savings to get here, are familiar with the inforamtion available on the internet.
While it is true that poor immigrants are the source of growth, the growth is at a price. The resources expended by the society is not in proportion to what is received in contributions by these individuals.
This is a contributing factor to the "downsizing" of the society.