I was playing in my minecraft server with my friends when I wanted to create a sword with attributes which used the multiplicative modifier (operation both 1 and 2), and it ended ut being worse than the normal when it had +120% attack damage. So we ended up concluding it had to be a bug because we tested with different swords and on different mobs, and the same result happened every time.

I don't know this for sure, but when using the multiply attackDamage feature I guess its supposed to multiply the current attack damage, including damage from the weapon you are currently holding because its what it seems like through the wiki and common sense

Here is one of the commands we tried:

/give @p minecraft:diamond_sword 1 7 {Unbreakable:1,AttributeModifiers:[{AttributeName:"generic.attackDamage",Name:"generic.attackDamage",Amount:1.2,Operation:2,UUIDMost:59115,UUIDLeast:160974}]}