Personal preference. I carry a full sized gun with no problem. I'm 5'8" and can conceal a 1911 or a HKUSP or a Glock 32 or a (insert almost any large framed pistol). It's all about having the right equipment.
-Inside the Waist band holsters can hide a whole lot of gun.
-Larger guns are easier to shoot for the vast majority of folks.
-They have a much larger capacity than mouse guns. (ever watch someone do a mag change under duress that hasn't practiced it before?)
-Shorter, smaller guns require more attention to detail due to the shorter throw of the slide. (shooting at the range will not be the same as in a self defense situation)
-Relying on the encounter to be close to you is a baaaaaad idea. (trust me, first hand experience)
-Pocket carry (assuming here that is what you are doing) is not very efficient unless you keep your hand in your pocket and on the gun.
These are just a few things I've noticed over the past 16 years of carrying a gun on a daily basis. Mileage may vary for some folks, but pigeon holing someone to one firearm because that's what they use is not really the best idea. Guns are a very personal item. There are brands that are better than others, but which model of those brands someone carries greatly depends on its intended use, fit, feel, function and lots and lots of practice.
Your friend may be very well versed and trust worthy, but I'll bet that his opinions are based on his preferences. Unless you are similar in background, height, weight, dress, job, location, vehicle, fitness....well, then it may not be the best preferences for you.
Keep an open mind, and stay safe.