I don't think size is the real issue. Both Parker and Garrett take hit ups in a far too upright position and the tacklers get underneath them and drive them back. This is simply a matter of technique. However we don't need anymore second rowers we need speedy outside backs.
Both of them need a few lessons from Jorge. Get lower to the ground and use their legs and butts more.
Someone has to teach all of them how to hold onto the ball during hitups.