The content reproduced in the question is basically exploring what happens if we suddenly bring the wing to the angle-of-attack required to produce some given G-load, while flying at some given airspeed. The value of lift given in both cases -- 4166 pounds -- is undoubtedly NOT the weight of the microlight aircraft. It is undoubtedly much higher than the weight of the microlight aircraft. We are NOT looking at a situation here where net force and net acceleration are zero, so this content really doesn't shed light on the questions being asked.
On the content reproduced in the question, it's not clear why the asker believes that that the red arrow points to a climbing situation and the blue arrow points to a diving situation. At any rate, the content reproduced in the question has nothing to do with the forces in a steady-state climb or descent.
As to the questions asked--
"Is lift force not supposed to be lesser than weight during a descent?"
Yes, both in a steady-state climb, and a steady-state descent, lift is less than weight. To understand this better, keep in mind that in the context of winged flight, lift is defined to act perpendicular to the aircraft's flight path through the airmass, not vertically. Similarly, the drag vector is defined to act parallel to the aircraft's flight path through the airmass, and to a first approximation, the thrust vector can often be considered to also act parallel to the aircraft's flight path through the airmass. As a result, thrust supports part of the aircraft weight in a steady-state climb, and drag supports part of the aircraft weight in a steady-state descent, and in both cases the wing's lift vector is reduced. To see the force vector diagrams illustrating these situations, visit these related answers to related questions:
What produces Thrust along the line of flight in a glider?
Does lift equal weight in a climb?
(Note-- to apply the vector diagrams shown in the first link above to the case of a powered glide or powered dive, simply replace the label "drag" with the label "drag minus thrust" –- much as the label "thrust minus drag" appears in the diagrams in the second link above.)
"Is descending at an airspeed much lower than the dive velocity (Vd) of the airplane affect the rate of descent of plane?"
Yes, for a given throttle position or a given thrust force or a given power output, if we change the airspeed, we'll change the rate of descent. In general the slowest descent rate is obtained flying just a little faster than stall speed.