In my opinion, djinns and spirits don't weigh anything; they are just magical vapor capable of manipulating objects.
Regarding the size of dragons, I initially liked the concepts:

(number 7, with a height of 10 meters)

In my opinion, the dragon in the last picture is depicted very realistically. I wanted to adopt a similar concept, with a weight of around 1500 kg and a wingspan of around 25 m, but Nival drew the dragons too fat and with a disproportionately small wingspan, only about 12 m (and even then, only for the light ones). A wingspan of about 25 m would visually cover the entire field.