I was watching this video and it shows that adding fins on the wing helps the air get turbulent on the upper part of the wing, which forces the air to stay longer, and ultimately this helps with lift.
To my understanding, if we didn't have those fins, the air wouldn't stick so long on the upper wing, leaving an "empty" space, with low pressure. So this should help even more with lift (lift = pressure from the bottom - pressure from above).
Is that correct? In other words, the fins help adding back "horizontal" pressure, and thus reduce pressure drag, although it makes the airplane lose some lift (which is ok because there is plenty)