Wait, what? You don't gain extra natural light in summer due to DST. The days become longer naturally due to the angle of the earth wrt the sun. DST makes you get up earlier to "enjoy" that longer, sunnier day, but that one hour is probably pointless in terms of mental health improvement.

Besides, summer isn't the time when sunlight is lacking. Winter is when people get vitamin D depressed, and no time change is going to fix that for northern countries.