Proficiency can be measured in some aspects of concealed carry, but not so well in others. Is Jerry Miculek proficient? At competitve shooting no doubt, but maybe not so much if having to dig that snub out of his pocket if a couple of guys jump him on the street. Is Cecil Burch proficient in integrated skills and H2H ability? He's definitely articulate and a good teacher of what he teaches, but I honestly wouldn't give him very good odds in most street-fights. Is Michael Janich proficient with a gun and blade? While another good instructor with a keen understanding and ability to translate concepts, I wouldn't like his chances in many self-defense scenarios.
Training doesn't always result into acquiring a high level of ability. You can get instruction and practice all you want at the best baskeball camps and under elite coaches, but that doesn't mean you'll actually achieve similiar skills as a pro-player or even get all that good. Fighting with a gun is really no different, but many seem to think proper training and practice can somehow can magically transform any individual.
Proficiency in relation to public safety is a concern, but most gun guys think only of stray bullets. What about situational awareness and weapon retention skills, so we don't inadvertently arm bad guys. Or integrated H2H skills to access the gun in close-quarter scenarios. Functional standalone H2H skills make sense so you have options besides only resorting to the gun. What about common sense, general cognition, mental acuity and intelligence levels as I do seem to come across a lot of stories about people forgetting their guns in bathrooms stalls as well as guns going off after being carried in a pocket with no holster. When is someone too old to carry a gun responsibly? I actually worry more about these things than individuals actual shooting skills.
There's no consensus on what it means to be proficient, there's simply too many variables to consider to clearly define it and why legislating proficiency standards is a difficult and often misguided task.