I'm not sure whether is this an intended feature but I just found that the game doesn't operate Items' certain Attribute Modifiers with the non-Player mobs' Attributes.

For example, using this command to let you and an Illusioner wear a same weapon:

/item replace entity @s weapon.mainhand with bow[unbreakable={},enchantments={levels:{flame:1,power:10,punch:3}},attribute_modifiers={modifiers:[

{type:generic.attack_damage,amount:16,slot:any,operation:add_value,id:base_attack_damage}

]}]

You and the Illusioner shoot a Wandering Trader for each in the same minute. You may find that you deal more damage 'an the Illusioner.

 

Or on the other hand, you can summon two same Illusioners with the weapon mentioned above but either with bigger "generic.attack_damage" amount. You may find that they may deal the same damage, or the one holds bigger amount cannot defeat the same enemy easier.