To be honest in game Saradominism is still the strongest faction in quantity.
May I point out that the amount of, lets say, Zarosians is currently probably smaller than the population of the town I live in?
Actually, I'm pretty sure Zarosians (unfortunately) outnumber Saradominists by a significant margin. But I haven't seen a poll in over a year, so I may be wrong. I believe he means in terms of in-game characters, there are far more Saradominist NPCs than any other faction. Most major cities have altars to Saradomin whilst altars to other gods are more out of place.
Hiya, I'm Zev! An Ice-focused Drakewing who wants to help out!