Those "Amish" style coops are much better than the majority of coops you see, but they are usually short on ventilation, have the ventilation in the wrong place, and the plans misrepresent how many chickens actually fit appropriately as badly as the prefabs do.
I have a coop that is designed to hold up to 12 chickens ( built from plans) and I have seven. The dimensions of the coop are 5 feet wide, 6 feet deep and 6 foot 11 tall.
Do those dimensions include the nests? If yes, you don't have a 5x6, 30 square foot, 7-hen, coop, you have a 4x6, 6-hen coop. That little difference may or may not make a difference, but it's important to know -- especially if the food and water is taking up space in the coop instead of being out in the run.
You don't need a square foot of ventilation per hen. It's complete nonsense as it seems you've discovered.
Having a general guideline is NOT nonsense. It's an important data point from which the chicken-keeper can use local knowledge and observed conditions to adapt the coop to his specific needs -- the goal (for those not in the most severe of sub-arctic conditions), being to equalize the temperature and humidity inside and outside the coop.
For example, in my climate a single square foot per bird is only adequate summer ventilation in the coop with the Monitor Roof and then only if the coop is located in the shade. I discovered this spring that I need at least double or triple that recommended minimum to keep an unshaded coop with a flat roof under 100F on days over 90F.
There's no substitute for actually measuring conditions, but the guidelines are a useful starting point.
The four square feet per hen is also unrealistic and often not required.
What's "unrealistic" about providing a flock with adequate housing? I submit that if a person can't afford to give their chickens adequate space -- either on account of building costs or lack of available space on the property -- they need to rethink their plan for keeping chickens.
Your point about 100% free range is valid, but expecting the average backyard chicken keeper to be able to 100% free-range their chickens over a generous area and to never have to leave them in the coop after dawn or shut them up before dusk and to never experience weather conditions that make the chickens unwilling to leave their coop is considerably less realistic than advising them to build spacious housing.
Of course the Usual Guidelines are *
guidelines*, not hard-and-fast rules.
@Ridgerunner's excellent article on the subject should be mandatory reading for all new chicken keepers:
https://www.backyardchickens.com/articles/how-much-room-do-chickens-need.66180/
However, though I admit that the plural of "anecdote" is not "data", in years of reading these forums (even when I was not actively keeping chickens), I am convinced that the vast majority of health, behavioral, and sanitation problems that people seek help for here are due to over-crowding and/or inadequate ventilation.
There is nothing that is made worse by ensuring plenty of fresh air and elbow room.
