@FFF:. .. .1st Error:. .“...I'm flying along, straight and level. Lift=weight, and thrust=drag...”. .This is a widespread myth. Because of wing & fuselage moments plus CG location effects, a downward elevator-force is required to achieve some kind of stability. Thus lift in s&l unaccelerated flight is always greater than weight.. .. .We have to differentiate quite precisely between the force created by the wing (lift?) and all the other forces acting upward and/or perpendicular to flight path, the sum of which support the vertical component of the total flight vector.. .. .Furthermore, it is this “small angle”, that makes a whole lot of difference in climbs and descents.. .. .To answer your confusion: The only thing you forgot in your calculation ref. drag is weight, which, in a climb, acts partially rearward, thus increasing the total force acting “against” the flight path.. .. .To be precise, during power-off descent, wing-generated lift is greater than during climb.... .. .happy landings