The Arctic region insolation absorption is very poor even in the summer
The above grapheme is correct. It shows the average 24 h insolation intensity and it is correct.
Since at 90° degrees there is at summer solstice 24 h insolation the average is some 520 W/m².
But it is a small spot on the globe.
Now let's consider the angle of incidence. On the top of globe at the summer solstice the angle of incidence is equal to the Earth's Axial Tilt = 23,439°.
When the angle of incidence is very low the incident solar flux is not absorbed, but mostly gets reflected from the surface to the outer space. There is only a tiny 10% - 15% of the incident energy is absorbed.
Now let's compare with the 30° degrees latitude.
There is some 480 W/m² average 24 h incident solar intensity.
But the angle of incidence is 60° + 23,439° = 83,439°.
The sun is almost at Zenith there. When the solar flux is close to the perpendicular, then almost the 80% - 85% of the incident energy is absorbed.
So the Arctic region insolation absorption is very poor even in the summer.
The faster a planet rotates (n2>n1) the higher is the planet’s average (mean) temperature T↑mean:
Tmin↑→ T↑mean ← T↓max