Each and every single trade in lane favors him, not in terms of outcome. It doesn't matter if he eventually dies once or twice as long as he gets to proc grasp of the undying which increases his shield strength. His W gives him more health just for farming.
Assuming the laning phase ends around 10-12ish minutes, 80-100 farm translates into 400 health from ranged/melee creeps and another 75 health from cannon creeps considering 4 waves. I wont consider the health gained from grasp because it's not unique to sion, but 475 health has a gold value of roughly 1200gold.
Also, that 475 health adds 38 hitpoints on his shield, which if not broken is translated into 47 damage at rank 1 W on an opponent with 1000 health. In a 3v3 skirmish scenario that is further escalated to 150 damage. Those values increase with ability rank.
Those are just the stats for 100 creeps.
If anything it synergizes even further with the grasp on hit for increased damage + heal.
I still remember when vlad got gutted back in season 2- if i remember correctly - because his passive was bonkers.
Please make it so that his shield at least scales with bonus health while adjusting the base numbers so the suggested tweak wont trash him completely.