Ezreal Manamune Q Doesn't proc on champions?

I went in a custom game to test some builds damage and it seems like the manamune activated damage is unnoticeable i was ezreal vs lucian level 18 no defensive items on him and manamune would give me all the bonuses it does + i had gauntlet so i tried out the damage i would get like a difference of 30 damage which is irrelevant if you're gonna waste alot of mana because it's activated might as well get another item but i thought this can't be right can someone run a test too?