I'm sorry, but I've been to places like you're talking about. Where there are 14 horses and about three acres. My horse was (briefly) boarded in one of those places. They end up being mud fests. I feel so sorry for the horses living there.
I understand the desire to have horses. I don't understand the desire to cram as many as possible in as tiny a space as possible.
I've only had horses at my place for about six months now. We have two horses and about 1,5 acres of pasture. I thought it would be, but it's not enough. I had to pull them off it early just to let it grow again by spring. Next year we will be fencing off 2 additional acres. So that will be 3.5 acres for two horses. And I think that will be just right.
I'm not talking about grazing. I'm happy to give them as much hay as they need. But what happens is they soil large areas of their small pasture. There is manure everywhere. Other than being a breeding ground for parasites, that manures obviously prevents the grass from growing. Then they walk in it and churn it into the ground. Before you know it, it's just mud. Once the roots of the grass die, that's it. Luckily, our pasture hasn't reached that point, but I've seen so many like that.
I think the one acre per horse is a bare minimum. I am actually aiming for much more.