There are obviously a lot of issues to consider. As previously stated, there is no guarantee that you're going to succeed if another DPM has, and there's no guarantee you're going to fail.
I believe that as per Kidsfeet's comments, there are other issues going on with your brother. Those issues can be in his personal life, professional life or both. He may be unhappy with the group he's working with, his own solo practice choice, the location he's chosen, etc.
Additionally, he may have insecurity issues that have to be resolved. The majority of DPM's in practice have run into some form of bias in the past. However, I don't get angry or insulted. I attempt to prove them wrong after educating them, and if they still don't "get it", I simply chalk it up as THEIR problem and ignorance.
If you're not confident in who you are and what you're doing, that can play a major role in your complaining. The majority of the time problems are perceived, but not really present. And more often than not, you have to reflect and determine whether YOU are at fault for the problems you're discussing and is it REALLY the fault of everyone else???
If you are presently happy with the path you've chosen, I would urge you to continue on that path. Learn from your brother's errors and move forward.
I know significantly more successful DPM's than unsuccessful DPM's. The few I know are always blaming everyone else, but don't see that their choices have contributed to their failure. They walk into a hospital with an attitude, like they are the foot & ankle surgeons who are going to save the world. But the staff at the hospitals deal with orthopedic surgeons, vascular surgeons, cardio-thoracic surgeons, neurosurgeons, etc., and are less than willing to put up with the antics or ego of a new attending. They already put up with the ego of those mentioned. Additionally, many of those I know who complain about not making a living, are also the docs who want to work 10-4 everyday, with an 1.5 hour lunch. They work no nights, never considered working on a weekend and don't make their office available to succeed. They WANT the patients to simply run in the door at the doctor's convenience, and the doctor simply doesn't want to compromise. I talk to these docs at seminars, and they have 25-30 hours of office hours during the week and wonder why they can't make a living. They don't prioritize. Going to the gym, going to Starbucks, getting home for dinner every night by 5, running shopping errands, etc., is not the road to success.
As far as any website with doctors constantly whining, please read the above. I've been in the profession for over 25 years, and don't know of ANY bright and hard-working doctor who has failed. None.
There is no easy road in any profession. If you are bright and hard working AND know how to communicate with other people, you should have a great future. I personally believe "ethical" also belongs in those traits, but unfortunately we all know unethical doctors in all specialties who have been successful......until they're caught.