I moved your post so it’s no longer off-topic!
That’s a really good question. Reducing data can be tricky and inevitably there is some loss of fidelity. Many parameters don’t change much over a short time period, and in that case “snapping” to the closest observation creates the “truest” line. But you’re right that this is not necessarily true for the solar parameters (UV, Lux, Radiation). Perhaps, like wind, we should display three values (high, low, average)?