Card may have more physical talent, but can it translate to the field? Can he pick up TR's offense? Is he a leader? Can he even get into ND?
Hartman doesn't have 5* tools, but he's above average physically and his intangibles make up for a lot of what he lacks physically, especially leadership.
Hartman has done what he's done at Wake Fricken Forest. Put ND talent and Oline around him and he'd be great.
Card may be great too, but he's a total unknown.