Kaya and other manaloss reduction items should instead allow you keep a minimum amount of your maximum mana from being burned, rather than just reducing mana burn things. Since for the most part you're still going to run out very quickly, especially against a PL.

Or it could be in an in addition kind of thing. I think the average hero has like 1,000 mana unbuffed even going into the later stages of the game, so if it's 15% of that you can at least get one spell/item/TP off after being hit by drains, of if you're int and your mana matters more, you can still maybe fight against mana drain heros.

or like for some reason you can built it on WK if you don't want to take your mana drain talent.