Something is definitely wrong with Force Blast:
1) It almost never knocks back. I've tested it on regular enemies and elites and it does not move them even a little bit. It only triggers the "get hit" animation. The only time I've seen a successful knockback is against the K3K necros

I guess if this is intended, the tooltip text should be edited.
2) The slow on enemy cast rate flat out does not work. I've got enough hard points for 50% enemy fcr slow and tested on K3K caster skeletons. Their casting speed is the same no matter if they are Force Blasted or not.
The damage reduction does work however.