There's is zero drive and zero intent in his delivery.
It doesn't seem like he is throwing very hard, from an intent stand point.
He doesn't stride, he simply takes a step forward.
The back leg plays zero role in his mechanics.
No matter what his stride length is, it shouldn't be a length that is a comfortable standing distance apart. He could stand with his legs further than his stride.
-Throw with much more intent
-Develop more separation
There are good aspects of his delivery too:
-He has good arm action(from what I can tell at full speed)
-Good upper body mechanics for the most part
-He's 6'4. Bigger lever is a big advantage.
I would suggest working on the following:
-Develop intent-Throw as hard as you can! Only those who desire and try to throw hard will.
-Stay closed longer. He front leg simple steps and opens with zero aggression
-Faster stride-Get the hips moving faster-this goes along with intent.
Just look at someone like Chapman, Lincecum, or Trevor Bauer. Look at their legs move in their mechanics.
Power starts at the legs. He's depending nearly all his velocity on what his upper body does. He needs a powerful stride, aggressive mechanics, and hip/shoulder separation.
My guess is that he's in the mid to upper 70's. Maybe 80 right now. With his big height and upper body mechanics, that should be much much higher.