Chuck looks huge! This mare is suppose to be 16.2-16.3. That is the only picture I have of her under saddle. I can see a video of her being rode not long ago but it is not one I can share. It is on the sellers fb page.
Just to give you some perspective, I am 5'6" and weigh about 130.
I definitely use a mounting block. If I ever need to ground mount, I find a 'ditch' and put Chuck in it so I can get up from the high side. It takes some grunting/groaning to climb the mountain! ;-D