Yes, the giant lance does give some boots on damage based on its weight.
However the weapon lvl and refinement part matters significantly.
Any +12 lvl 4 weapon will give {4*(12+6)*100} = 7200% which is way higher than the 2000%.
Using the giant lance, you'll need 120 str to have that 300atk bonus, which isn't good unless you're going for extreme build i.e.120 str, 120 luk...
Pros: -heavy weight
-high damage at 120str.
Cons: -No shield, need to depend on millennium shield for defence or switch gears.
-No bonus damage on demi-human.
I would say get a high refine glorious/bellum spear and test it out in pvp first.
Most classes have high reductions so you'd probably want glorious/bellum weapon~
Also CS have high chance breaking the weapon.
You can use two hand sword too, glorious claymore as an alternative weapon, that way you're able to cast parry as one of your defences.
If and only if you're one of those crit addict and financially capable, get a high refine Violet Fear with sharp enchantments [1Thanatos, 1 randgris] <<<this tend to be more of a PvM weapon
Don't forget to use Giant Growth and Fighting Spirit before you CS someone/something~ have fun