Your mistaking making guilds profitable overall and making it profitable for a one or two people. SA for instance (religions are guilds) could definitely be profitable for leaders because of a lot of donations by a lot of people. Is the guild a gold sink? Yes, but it can still be profitable for a some people.
I'm not an elder to confirm anything on SA's financial situation, but I really doubt that SA can make anyone rich. If you want to be rich, try to get elected as lord of a city in a realm with a large food surplus. Fiddling around with guilds is not the way to go.
Sure, it's possible to be a total leech and get more gold out of guilds than you put in, but that will never make you rich.
