Well, yes, 8% difference in pay is substantial. Drinking 8% more water in a day just means I pee a bit longer at some point.I won't go through them all.
0.29% compared to 0.37% is a large difference.
To make this clearer remove the zero and decimal point you get 29% and 37%.
If ones pay packet increased by 8% most would consider this as a substantial pay rise.
For Methionine, there isn't a single percentage that is optimal for every stage of growth, different amounts are needed during times of stress such as during hot weather, and different amount are needed depending on how much cysteine is consumed. Met is used to make cys but if there is more cys in the diet, it doesn't have to and can be used for the other things it does.
National Research Council says the chicks 0-3 weeks old require 0.50, chicks 3-6 weeks old require 0.38 and chicks 6-8 weeks old require 0.32%. Setting three week intervals is arbitrary; they don't flip a switch the change to need the next requirement. Even if you feed a different feed every three weeks, some will get a bit less than optimal and some will get a bit more most of the time.
If it isn't optimal, the difference from optimal shows up in growth rates if it is a small enough difference. It shows up in feather picking and cannibalism if it is a big enough deficiency. On the other end, growth rates start slowing at 1%, so that helps dial in the window of acceptable.