Good post. I believe "reasonable" is a good base for judging performance.
The struggle for many of us is the individuality of each scout in their effort to perform. I'm not one who cares one way of the other about "adding requirements" because I respect the challenge of judging a scouts performance. But, I do like to caution scouters that as soon as a fixed rule is set in stone, it will be challenged with an unexpected situation. It's great to add a hard expectation to draw lines between success and failure. But at the same time, these rule often restrict creativity of unusual situations.
I typically ask adults, what is the troop gaining by adding requirements like the 50% meeting rule. I mean really, how did they come up with that number. But, I understand that some added rules or guidelines are needed for a unit to move forward, especially new units. However, at some point the unit should mature past the added rule and used their hard earned wisdom to judge individual effort. I had a 15 year old Life Scout volunteer to run a Boy Scout Skills day for a Webelos leader who had requested it. He knew exactly what to do and was excited about it. But, he informed me two weeks before the event that he couldn't be there. However, he promised he would make sure the event would occur as planned. And it did. The Den Leader said her scouts loved it. Now, was that scout irresponsible by not showing up to an event he promised to lead, or should he be complemented for his performance delegating, training, and planning a very successful activity. By the way, the scout didn't ask for, nor did he, recieve any credit for the activity. Well, I did brag about him a lot. His dad is my neighbor and is a little tired of hearing about it after 20 years. That scout has two kids now after all. Still.......
When general rules are set for groups of individuals, individuality will eventually force the rule to get in the way of the main objective.
Our troop pushed the PLC to take as much responsibility as possible, so they also would set rules like the 50% rule, or discipline rules, or something to help them in their responsibilities. But as the scouts learned and matured, the rules were replaced with wisdom.
Always keep and open mind so the path to the goals is always clear.