Spear Attack: XXX
Shield Attack: (DEF × 5 + SCR_Get_SklAtkAdd_SynchroThrusting)
Attribute Attack: 0%
AoE Attack Ratio: 1
if my logic is correct the shield damage depends on your defense multiplied by 5. Which would me just stacking defense items and skill means SychoT. deals a really big burst damage.
or info still isnt 100%
what you say it’s in part right. but you still need to watch you spear atack for more burst dmg, if i got the description right.
i think the attribute lets you have half damage on the shield attack for higher on the pierce one.
Ooops I fixed the description to display the 2nd attack value correct 
Afaik the shield damage indeed scales with the DEF but probably only with the DEF value of your shield and not your overall def value but someone needs to confirm this ingame as I’m not 100% sure.