The wind speed was measured a few meters above the ground, and the flights were carried out at several hundred meters altitude, if I was not mistaken in reading both documents.
The wind must therefore be much stronger at the height of the kite, which would considerably reduce the real efficiency such as measured with a wind speed close to the ground.
See the wind curve between 10 m height and 150 m height.
See also the second paper, figure 15, and page 20:
During a specific measuring campaign, an uninterrupted automated flight of 42 hours featuring day and night flight with an average power production of 62 kW has been achieved, in wind conditions varying between 4 m/s and 13 m/s (one minute average measured at 10m height) and estimated wind speeds at flight altitude of 6 m/s to 19m/s, showing the robustness or the implemented flight and power cycle automation algorithms and all system components at relevant load condition.
The measured power is based on the height of the mast (10 m), with an average wind speed of 12 m/s, among wind speeds varying “between 4 m/s and 13 m/s”, and apparently not the “wind speeds at flight altitude of 6 m/s to 19 m/s”.