@GraemeS , I can understand your frustration but I honestly think that you're painting too black and white a picture in your thoughts above.
Of course, you're absolutely right that referees at all levels can sometimes struggle to get a very strong assessment because the game wasn't 'difficult' enough. And this can impact overall because of the limited number of observations each season.
However, from my experience, if a referee is fully aware of the competencies he is expected to demonstrate, most games will provide a multitude of opportunities to show off many of them. Sticking with your examples above ...
1) Fitness. There are always times when that 'extra sprint' will be necessary / useful or where a forward is closing down the keeper and you can make the effort to get close just in case something unexpected happens
2) Corners. I can't remember the last time I officiated a game where there wasn't enough grappling going on at one of the corners to justify having a word with two of the players in order to stamp it out
3) Advantage. Almost all games have enough fouls to allow you to demonstrate the
choice as to whether or not to play advantage
4) AOL. On this one, at 7 to 6 and 6 to 5, simply getting ALL the basics right in every game will tick plenty of competency boxes. Substitutions correct, kit check correct, cautioning choices and procedure correct, injury procedure correct, Technical Area dealings correct etc etc
And the same is true on other critical areas like Match Control as well. Is the system flawed, hell yes! Fatally so? Not in my opinion.