Why remove mana and energy costs but keep health costs?

vlad is broken enough as is (in urf)

because all health cost champions are healers and they want to reduce healing. All the health cost champions would be literally unkillable if the costs were removed. The costs being reduced actually helps them out probably more than it should. The only one that doesnt really benefit, mostly because hes bad, is Aatrox.

Giving Soraka a secondary healer completely nullifies her health costs and enables her to become an absolute menace. God forbid you manage to find a game without a Sona ban, run the two of them and giggle at the ridiculousness. If you can't get Sona, Nami is probably the next best healer followed by Taric and Nidalee. Even though Nami's Q and E aren't the greatest for URF, her W is pretty outrageous on that low CD with no mana cost.

URF is all about health sustain which makes Sona, Soraka and Nami incredibly effective.