I don't think ravenous is that much of an issue. Kasadin, Zed and kata don't even get that much out of it, and ryze has plenty off other issues anyway.
I also don't think it's a big factor on Aatrox. Don't forget, unlike conqueror, ravenous only is 33% effective for aoe. so it's only ~4.6% heal on most skills.
For Aatrox with conqueror, he heals for 45% of his damage already, so it's ~9% more healing compared to without it(49.6% instead of 45%), so revitalize gives him more healing below 40% hp ontop of better regen, more healing from the passive and more healing from allie heals. Add in a deaths dance and ravenous gets even less relevant for him.
It's rarly a big factor for laneing when sustain is the most impactfull due to the stacking part(unless an early bot fiesta escalates or something), and later on most champs usually profit more from the other options.
And if Zed can't go for other options despite wanting them cause of mage harras, isn't that more a sign that mage harras is to oppresive and zed lacks other options against it?
Though in my ecperience a good zed can easily go without it and get the better options...
I also don't see how one can complain about the spelvamp rune but be fine with legend bloodline, the 12% lifesteal that can be obtained just by farming are much more impactfull and already have sigifican't impact in lane where it's often at +5% befor the first item is finished, which paired with a dorans and conqueror adds up to alot sustain.