"but rift herald does less damage the less health it has"
oh yeah because right after grabbing a rift herald, top and jungle who took it are gonna be like "welp might as well back off and let it do all the work"
no, what's really gonna happen is rift herald will show, and top and jungle will show up to zone laners away from it until it can charge up on tower and take 50% of its hp in one shot.
i don't see any clear counterplay to rift herald other than getting it before other team does. this is gonna cause a TON of problems. especially so for premades vs randoms. even duos vs randoms will have a massive edge if they go jg and top because of the coordination
could manage. though I am unaware if baron and herald go together....