Hi, kitsunegarcia!
I can not bend left pinkey without ring finger flexion (see the figure below). And my friend, whom I taught ukulele, can bend both pinkeys very well. Hence these flexibility may not mean much about ukulele skills.
We had a ukulele lesson today, and he could play F (2013) very well. I really convinced that this is not the flexibility or skill of the ring finger. It is rather the angle of the wrist today.
Photo I show the difference of the angle of the wrist between me and him in the figures below. The left column shows his wrong shapes of wrist, hand and fingers. The right column shows right shapes. I use easy C G and basic F chord (2010) for comparison.
1) A is the wrong angle of the wrist. B is right one and straight. This straight wrist is seen on Jake Shimabukuro, James Hill and George Harrison too (see the photo in previous post in this thread).
2) C and D show C chord. Even such easy chord, his wrist was flexed and his ring finger does not flex well, his hand shift to headstock side. Wrist should be straight like Jake, James, George and figure D.
3) E and F show G chord. As seen on E, his wrist is flexed and his hand shift to headstock side. Wrist should be straight like photo F, and fingers (index, middle and ring) should keep right angle to strings without shifting to headstock.
4) G shows the reason why our hand should not shift to headstock side. Ring finger and pinkey went off from the fretboard in this shape. He had a trouble changing chord on G. H shows basic finger rest position on violin and guitar. This rest position gives save intervals between each finger and strings. In this manner, finger nail should face to our face.
5) I shows wrong direction of a finger against strings. This direction is hard to control clearance to next strings. J shows right direction of a finger. This direction gives very fine control of finger tip with flexion of the fingers. Hence wrist should not flex, hand should not shift to headstock side and nail should face to our face.
6) K shows his wrong shape of F(2010). Wrist is flexed, hand shifts to headstock side and index finger can not flex well in his style. Flexed wrist prevent finger flexions seen in this photo, because wrist gives another pulley for flex finger muscles when flexed. L is right shape. Wrist is straight, finger nails face to our face.
After he's got a straight wrist, his ring finger climbed on the fret board (See the right figure below). Then we try to exercise lever (red arrow on the bottom figure) in order to see the direction of finger power by elbow. This lever is made by ring, thumb and elbow.
Even he's got the right shape (right figure above), he still need a conscious power of the ring finger in right direction, because ring finger requires elbow power.
He was very happy to get F shape and enjoyed today.