(warning, long rambling post, might be repetitive and have errors)
The way to resolve the problem of people who have good metabolic health telling those who don't what they can and can't do is resolved by proportioning one's beliefs to the empirical evidence. That means not being a bunch of know-nothing loud-mouths who lost some weight one time or (usually) are in the process of gradually losing weight and repeatedly share what they did, or what they think they did that produced/produces the results. When people talk about changes in their diet and effects, they always neglect to portray the whole picture. There are tons of different factors that change with each dietary change and people are generally not going to be objective about what they changed unless it really is one simple thing at a time, give it 30 days and see. Did I cut out nuts and my tummy felt better so I started getting more exercise but then attributed the results to the lack of dietary nuts itself? People are going to attribute their results to the factors that their minds become fixated on, not necessarily what actually caused the changes. This tunnel-vision isn't a bad thing, everybody has it, but the lesson is that anecdotes should only be given so much credence. And of course it has been mentioned that different biological states require different measures, and there will be some differences.
The grand solution is to get very specific lab tests and understand the mechanisms that produce the metabolic syndrome (better term than leptin resistance, which is one part of it), and then understand how diet and lifestyle impact on processes that produce a dysfunctional body. That is pretty hard for most people to do, and most people just want to get results and go about their lives.
The softer solution is to be patient and strive for health first. When people ask the question "what is going to get me as skinny as possible as quickly as possible?" they are doing themselves a huge disservice. It was likely years and years of junk food and chronic stress or whatever it was, that got you into this whole thing in the first place, what makes you think that you are going to drop 100 pounds by the end of the year with X Diet or Y Diet and everything is going to be peachy? The better strategy is to study nutrition and holistic health with an open mind, make at least an effort to understand some of the nuts and bolts of how everything works, and start working towards as healthy a diet and lifestyle as you can reasonably manage. Approach it from the "I want to live forever" stance, not the "gimme results" stance and the underlying problems of the metabolic syndrome will start to resolve them. Get passionate about health and knowledge about how to produce it and become what Byron Richards calls a Health Asset Manager. You manage your own health and you take complete responsibility for it. Robb Wolf doesn't take responsibility, your doctor doesn't take responsibility - they help and offer guidance, but this is about the person living inside the skin of the body with the metabolic syndrome taking charge for it and being the arbiter of what is ultimately healthy. Deferring to a particular diet book is oftentimes helpful for some, but an understanding of all of the things one can do to improve health is the ticket. Most health authors and originators of diets, even most people on health forums are dogmatic monomanics with emotions tied to everything they believe. That's not to be condescending since I do it too, although try not to. I'm not targeting paleohacks or anyone in particular, it is just the fact of the matter, that pretty much everyone I have ever read anything about nutrition from is not telling the whole story and are biased in favor of certain beliefs that make them happy.
Health first is the best ticket. What are the benefits of healing your gut? What heals the gut? How does this mechanism work? Glutamine makes the junctions in the gut tight by increasing zonulin. What's zonulin? Il-6 damages the gut, what's Il-6 and how do I reduce it in the body? You don't have to be a biologist, just listen to those who are and get a general idea of what they are saying and what the evidence is for what they are saying.
Coming back to evidence, there are a lot of unsubstantiated beliefs throughout the whole natural health movement, more concentrated in some places than others coughveganscough and it isn't helping things. Luckily there are plenty of bloggers and authors working on this so it is attainable to everyone. Join the movement. Not the "Mark Sisson's Primal Diet Is The Best Of The Best And Solves Everything" movement, but the one where people come together to discuss the evidence for what is healthy and how we might use it to our advantage. The diet mentality kills opportunism. There is so much supplement hate and nobody things they should have them, but scientists have been able to isolate powerful nutrients like curcumin to high potencies that have a profound effect on metabolic health. And yet people hate supplements. People around here hate fiber but good quality fiber has been shown time and time again to improve metabolic health and help people lose weight. High doses of it like 30g a day.
Gary Taubes wrote in his book Good Calories Bad Calories that it isn't unreasonable to assume that the same things that cause cancer and heart disease also tend to cause obesity. It really is all one metabolic syndrome and what people die of is oftentimes a coin toss. There is much better information available on the prevention of diseases than on using pure diet to impact things like hunger, the propensity towards higher and more potent but unsatisfying food reward, and decreased energy and vitality, but the causes are generally all the same.
The soft soft solution is just to eat unprocessed food, do the basics like getting enough nutrients, don't do anything to mess things up like exercise like mad on a 0 carb diet so cortisol skyrockets, avoid toxic things, and get active and fit with a good attitude and overall lifestyle and be patient. Oh I've been on the paleo diet 2 months and I have only lost 2 pounds and I'm doing everything right. Well sometimes it takes a long time for everything to get to where it needs to be. If people are so impatient they should try to be satiated and active on a lower caloric intake and although I don't think that itself is a great long-term strategy, the very act of losing some weight can mitigate the metabolic syndrome and be a springboard for the rest of it to start working. How long does it take to resolve dysbiosis, cells packed with omega-6, crapped out liver, nutrient-deficiency, leaky gut, etc. The answer is certainly not a few months.
Last point is to be a skeptic and learn to love skepticism. We can't ever really know if anything we believe is true. We have good reason to suspect many things are true but we might be delusional or be seeing with tunnel-vision or a blind-fold on. And it is really hard to tell with so many factors going into metabolic health what is really working if something is indeed working. So this all means that we need to be constantly questioning everything and revising our positions with new evidence. Always learning, and always working towards a better way of doing things.
In short, dietary advice needs to be evidence-based. Pure knowledge gets things done and Skinny Dude X needs to supply some good evidence for assertions and Not So Skinny Dude Y needs to demand it.