Irrelevant. The confidence interval is for the uncertainty of a parameter, the overall mean/trend: if most of your points fell inside it, that would not be good

Irrelevant. The confidence interval is for the uncertainty of a parameter, the overall mean/trend: if most of your points fell inside it, that would not be good but extremely bad (you have that much imprecision that your estimate of the overall mean could be anywhere inside the range of observations?). Ideally, your CI would be so narrow that ~0 data points fell within it. (An example: you take a population census of adult heights and find the mean height is 5'7 ± 0.001 inches, say. Very few people will fall within that CI. But that's because it's such a good precise CI due to so much data, not because it's a bad CI.) You seem to be thinking of a predictive interval (https://en.wikipedia.org/wiki/Prediction_interval https://en.wikipedia.org/wiki/Prediction_interval), which, however, is not what is being plotted here.