There was a previous bug report about RoG shields not generating a debuff effectiveness bonus which got fixed, I noticed the same thing with weapons besides staves.
Below is a screenshot from live showing that it should be possible to have debuff effectiveness on weapons:
Weapon RoG - debuff effectiveness
Weapon RoG - debuff effectiveness
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Re: Weapon RoG - debuff effectiveness
With season 3 around the corner, this could be a good fix.