I am going to politely ignore a bunch of the blasting of this guy due to his being Army, a gun snob, etc. His opinion is based on the equipment he gets issued (which he doesn't buy, to include hammers, unless he is also a contracting officer) and the training he received and now gives, which is extensive. He also appears to have practical experience. He is a product of the system, just as some are of other systems, which means he has confidence in the systems which he uses and teaches, it's necassary for success in his environment. A guy like him is going to pretty well look down his nose at anything other than his world, just like another poster has done the same to him. My point is, if you asked his advice, he probably wasn't the right guy to ask. If he offered it without your asking, it's the aggressivness that he has been taught as an expert in his field, but still more than a little impolite. In an environment like Afghanistan and Iraq, I can promise you that a forward assist and an ejection port cover are important items indeed, just as they were in Vietnam where those requirements came into being for a variety of reasons, one of the being mud, sand, water, etc. If those items are not included then they it can't be considered mil spec, since those are mil spec requirements, whether you agree that they should be there or not.
However, that is not to say that anything is wrong with your AR sport. It has some features not included because they are simply not necassary for it's intended use. The fact that you were able to shoot it, well and with no functioning issues pretty well prove that. A better evaluator of your ARs performance is other users of the same weapon and your own experience with it. Unless you plan to take it to the mideast or somewhere else, I wouldn't worry about his comments, but he really shouldn't have been that critical, but his view is a narrow one; it has to be in his environment, but he should learn to be a little more open minded. For myself, I've always been careful not to be openly critical (no matter what I may have thought) to friends and relations about their personal firearms, unless I spotted a legitimate safety issue, which rarely (if at all) happens with a modern weapon like yours. I always thought it was better to point out advantages and design strengths. If you are comfortable with the quality, accuracy and are proficient with your AR (which sounds like is the case), then you can disregard his comments as "prima dona" isms, something that all experts have an annoying tendency to practice. You have a good weapon there, and since you know how to use it, don't need to worry about absolute comments.
I routinely shoot and converse with an old US Army Ranger (Vietnam era) sniper trained retiree that currently is in charge of a European sport shooting team, and I know he would never make such comments. Chalk it up to a "whatever" experience. Enjoy your rifle!