I totally get what you're saying, but I think the problem is that your distribution is skewed, so that players you consider "average" are considered "good" by most other people. You've pushed your interpretation of average quite high up the ranks, so there is now very little space for the breakdown above that, of "good", "very good", and "world class" as you put it. This is demonstrated by the fact that you rate Fraser (a guy who last season created more goals and big chances than almost anyone else in one of the world's top leagues) as just being "good", rather than "very good".
In addition to this, both Scotland and Celtic (teams you would rank as average in professional football) both have rankings well above the actual average in the game. For what it's worth, many people do the same thing with movies. Ask someone to rank a movie out of ten and if they think it was average they will give it 6/7 out of 10 instead of 5. I call it the "imdb paradox".
Finally, the problem with Scotland fucking up against smaller teams like Georgia and Kazakhstan, isn't as simply put down to raw technical ability of the players as you think. A lot of it is mental, as with all sports, and Scotland have developed a real losing mentality which seems to rear its head most when we play teams we're expected to beat. You as demonstrating some confirmation bias in not also pointing out that these same players who have struggled against the world's worst teams have also often had amazing games against some of the better teams like England, Spain, Croatia, and Germany in recent years. So ask yourself, do they suddenly acquire more technical ability on those days, or could it more likely be down to mentality and coaching?