It’s not so much height as it is length.
Leonard has 34 3/8 inch arm length. Elite for the position which helps him disengage from blocks to make plays.
Wallow measures 30 7/8 which is t rex like for the position and the main reason he dropped to the 5th round. Hard to beat NFL blockers with short arms.
“ Something of note: 13/67 NFL LBs have Arm Lengths shorter than 32". Ironically, this list doesn't include Shaquem Griffin, but he wasn't recorded due to his unique situation (The longer arm is 32 1/8").
Of those 13 Linebackers, only 3 have been selected for the Pro Bowl. This list is Luke Kuechly at 31", Joe Schobert at 31 1/2", and Kwon Alexander at 30 1/4".
Kuechly stands to be the greatest outlier in this. At 31", his arms are shorter than you would expect of a DPOY and potential HoF LB (All previous HoF LB of the 2000's and Patrick Willis had 32" or longer arms). His rival for "best MLB in the the NFL", Bobby Wagner, has longer arms at 33”.”