Ideas:
The Nether Star will have a White Boss Bar, Will Lose 1 Point when a Wither Skeleton Raider Dies
When a Piglin Dies and there is at least 1 Wither Skeleton Raider, It will absorb one of them and Regen the Boss Bar by 1
When a Piglin Brute Dies and there is at least 5 Wither Skeleton Raiders, It will absorb five of them and Regen the Boss Bar by 5
When the Raid Successes, the Nether Star will became a Wither, and then Kill EVERY Remaining Wither Skeleton Raider
When Enough Wither Skeleton Raiders Dies(160), the Nether Star will drop and became a Gilded Star, Applying Effects by Throwing It on the Ground with Specific Minerals and put it in inventory instead of Crafting a Beacon and Make the Huge Base, Same Effects can be stacked to have lv2, Diffrent Effects can Stack
When ever 40 Wither Skeleton Raiders Dies, the Wither Army will became Stronger(wont last to next raid):
40-79: Netherite Swords and Power 2 Bows
80-119: Netherite Helmet(50%), Netherite Chestplate(50%), Netherite Axe(50% replace netherite sword), Power 4 Bow(50% replace bow)
120-159:Netherite Helmet and Chestplate(100%), Netherite Leggings and Boots(50%), Netherite Axe(100%), Power 4 Bow(100%)
Mineral List:
Redstone->Regen
Emerald->Jump Boost
Lapis->Speed
Gold->Haste
Amethyst->Strength
Diamond->Resistance

Nice photoshop in the second image :)
But hey, good job!

Is there any way to win the raid? Some piglin benefits would be quite interesting. That being said, this is EPIC! (P.S. Perhaps doing this would turn piglin heads in the bastion into wither skeleton skulls? Would be an interesting farming mechanic.

Good job friend, nobody makes datapacks like you, thank you for so much and sorry for so little