To answer your first question: As a tank how does it feel to you to chase down a foe you knocked away? To me it feels pretty ok. My first tank on live was a WarMace and we knocked everything away or up, and no one cared. Until I teamed with a burn tank then he cared, what-ever. Yeah, I wasted a burn patch, but so what. When I play a blaster and I knock something away, I own that guy until he's at zero health. So you don't need to concern yourself about chasing him down. You can if you want to but you don't have to.
EDIT: The only powers that need KB/KD, imo, are pets that do knockback. Like some controller pets, or masterminds.