>> I dont have a dog in this hunt
> Well I do
Well then what's your stake here?
> he has a tendency to try to dismiss differing points of views on the basis that he has 20 years of experience
I surely will concede I have this tendency, now you have to keep the context in mind. You are on an internet forum focused on CS, and emerges a comment thread on personal investments. The very subject of this thread is whether it makes sense to consider risk adjusted returns or just any kind of returns for your investments.
My argument is based on the fact that risk adjusted returns should be used, and you should assume normal distribution. I am not saying this is a law of nature, but rather that this is a fine and widely used assumption for both practitioners and academics, which allows the argument and explanation to go further without entering an experts debate (like you are trying to start).
So I stand by what I said: for all intents of this discussion, assuming normal distribution should be a given. If you want to dance around it and demonstrate that a students distribution or whatnot is a better fit, go ahead. I think this is more armful than helpful here.
> try to dismiss differing points of views on the basis that he has 20 years of experience
I think this is important on the contrary. What is lost on a forum like HN is the context of people answering comments. When someone comments "I don't think risk adjusted returns are important", it makes a hell lot of a difference if it's just the opinion of a random guy, or someone with actual experience.
Now while it takes 1 sentence to wrongfully dismiss a scientific fact, it can take 100 pages of an expert to prove that it's true. Look at a proof that 1+1=2.
That is where credentials are important IMHO. Some debate tengents are not interesting in a discussion, and will only lead to an expert explanation serving no purpose other than confusing a reader, and making the expert proud of himself. In these situations, just stopping the tengent is the best reaction IMHO.
So I apologize if you take my comments as dismissing, but try to assume good intent. When someone asks why you should use risk adjusted returns to compare investments, I think the saner thing to do is to tell him to assume normal distribution, because that's the far more likely scenario, most of the research do take this overall assumption, and you can proceed to the demonstration that makes sense, which I showcased in my previous comment about 10% returns on 10% annual vol versus 5% returns on 1% annual vol.
To re take the example I posted above, when the discussion is about 1+1=2, I don't think you're doing any good contradicting that it doesn't hold on Z/2.
Assuming normal distribution of returns is a pretty standard base for comparing investments. It is a base shared by many models and metrics. Sharpes don't make a lot of sense on non normal distributions, mean variance optimization either.