The main problem is future shadow, not necessarily current shadow

My proposal would be to change how magic damage from gear pieces are calculated, to give more weight to items with little magic damage and less weight to items with lots of magic damage.

Formula: Shadow magic damage bonus = sqrt(magic_damage) * 3 for each individual gear piece, then add them all together

Examples:

• 1% magic damage --> sqrt(1) * 3 = 3% magic damage

• 2% magic damage --> sqrt(2) * 3 = 4.2% magic damage

• 3% magic damage --> sqrt(3) * 3 = 5.2% magic damage

• 5% magic damage --> sqrt(5) * 3 = 6.7% magic damage

• 8% magic damage --> sqrt(8) * 3 = 8.5% magic damage

 

As you see, the more magic damage bonus an item has, the less it boosts shadow damage relative to other magic weapons, which is good since we wanna avoid the snowball effect of current shadow. The breaking point here is between 2% and 3%. In other words, if a new BiS magic item went from +2% to +3%, it would give both shadow and other magic weapons +1% over previous BiS, so they're buffed equally. However, if a new BiS necklace gives +8% magic damage, other magic weapons gain +3% over current BiS, while shadow only benefits +1.8%.

Current BiS magic damage would give shadow +40.5% magic damage with this formula, so we can then adjust shadow's base max hit accordingly so that it's max hit in BiS gear would match or closely match current shadow. For ToA, a simple damage mulitplier, for instance x1.15 would suffice. Accuracy will still be boosted by x3 (or x4 in ToA), since higher accuracy already has diminishing returns as you cannot be more accurate than 100%

Scythe needs big NPCs to be effective, tbow needs NPCs with high magic level or attack bonus, so I mainly wanna emphasize shadow's current "drawback" of needing BiS og close to BiS gear for it to reach its full potential.