The main problem with Cultist Sacrifice is that it's two items hiding under a trench coat. It's both for late game carries that want to scale, which is apparent from the fact that it gives passive farm speed from Monster Rounds, and the item scales with boons becoming stronger as the game progresses.
But the item also wants to be a quick powerspike for heroes that don't really want to spend a lot of time farming, which is why it lets them instantly consume a T3 creep and gain a level up and a buff that they can use to try to impact the map.
In my opinion the item should focus on only one of those goals, and primary lean towards the early impact playstyle, and thus shouldn't build out of Monster Rounds and give passive farm speed. Also the buff it gives you should be completely flat and not scale with boons, and it could give stats like Move/Sprint Speed, Bonus Health, Fire Rate and or Spirit Power, which are all useful for maximizing your early impact.
Then if desired a second item could be created to replace the other use for Cultist Sacrifice, which is passive farming. This item could build out of Monser Rounds, give out of combat regen and other stats which are useful for heroes that like to farm.
