You misunderstood.Neither is true. Enemies don't need to be over 30 and your light level doesn't make a difference either, as long as your equal to or over the enemies. Weapon attack doesn't work like light level. People kept insisting when Dark Below came out that you needed to fight level 32 enemies to make a difference with 331 attack weapons, but it made a difference on any enemy above level 22.
Your light level absolutely 100% makes a difference, up to the level of the enemy.. which is what I was referring to. And the jump from 300 to 365 IS significant, assuming you're at the appropriate level.
No, using a 365 vs a 300 gun on a level 35 enemy isn't going to help much when you're level 22, but it will help a ton if you're level 34.