“A family with more than 6 kids with only a father in kollel and maybe a mother making a little extra cannot expect to send their kids to yeshiva, pay bills and dues, donate to tzedakah, and afford good quality food and healthcare.” — No but they can expect to earn enough to eat but maybe they’ll have to skip the junk food, nosh and eating out. They’ll be able to afford adequate health care, at a level that the Hafetz Haim would have considerable unbelievable – but not a fancy doctor with the latest experimental medicine. No one expects kollel families to play an important role in terms of financing community institutions (but many provide very useful warm bodies to actually get things done). Most frum organizations adjust fees based on ability to pay (one might aruge that if it doesn’t it isn’t really frum).
So do you mean they’ll live like families that afford a large detached single family home in Brooklyn, a second home in the country, full tuition (and all the protectsia that goes with it) at the fanciest most modern Jewish schools, a really fancy doctor who doesn’t let cost bother him in practising in medicine, etc. — of course they won’t. And if someone’s goal in life is a high level of material goods, they will do something else for a living (and if the past is an indication, they will give up a lot in terms of Yiddishkeit to do so). Jews who consider gashmius to be a principle goal rarely stay frum all that long – remember the mere act of keeping Shabbos, wearing a kippah, eating only kosher and living in an unfashionable neighborhood (i.e. one with too many frummies) means giving up perhaps 2/3 of your parnassah.