Its already been broken. That scaling bug was actually over the top- try like 400mil thorns instead of 44 mil thorns in T4. You can still get pretty high Thorns number, since Thorns benefits from primary stats.
Do you only need to be attacked to trigger thorns, or does enemies actually need to do damage? If the later, it seems counterproductive with high block.
You simply need to be attacked. Blocked/Absorbed/Dodged hits proc thorns damage.
I have to say that this would be extremely power with Hack.