Just say "Reduce target creature's attack by 3". It's pretty confusing otherwise. It's still pretty weak compared to the rest of the CC in the game, but...I guess it's insane compared to light's other CC (read: none).
Unless you're fighting
and just happen to have holy light on hand
... but ya, thats pretty useless (although in the 1.4 beta where you can have some control over your opponent it might see use...) ...
is not known for CC.
This could be interesting in conjunction with AM, assuming it will be able to further reduce the ATK after it is already negative.