That is the bottom line - plus the stress and now a court case. I do not think he was being greedy either - someone came to him with a proposition which wad flawed and builder is out of pocket and he breaks even. Valuers got it wrong but he was part of the risk taking
He is over 18, an adult and all business deals you have the potential to not get what you hoped out of them, it is called risk. If he can't take the heat, don't enter the kitchen. The trouble with taking the other party to court is also a risk, should he lose he will have his legal costs to pay and the other parties costs might also be awarded against him. All court cases have a bit of a lottery element.
It looks to me that mistakes have been made where he has only broken even in a rising market and he must be a party to those mistakes as caveat emptor applies in all situations and unless the other parties have behaved very badly then IMO he also has a duty to make sure the numbers work, not only for him, but also for the other parties when it comes to financing the plots development.
At the end of the day, much as it is painful to lose money, there much more important things in life, like families, friends, good health etc, etc and while we are healthy we can all work hard with vision to make some more.