@Repertoir If Rand's has to Lose it's Crit Reduction

And your goal is to position it as the most statistically relevant of the armour/HP items, why not go all out on this idea?

One of the major problems in tank itemisation is their lack of any option to opt into more expensive items effectively opting into a more late game based build. Based on what you said about Randuin's

The idea behind Randuin's was to position it as both the most defensive and the cheapest option of the primary Health/Armor items, but it seems like players would prefer it had ~300g worth of power put into it so that the reason to pick it over Sunfire/DMP is much clearer and more satisfying

it seems like a perfect candidate to fill this position amongst tank items. All you'd have to do is not put 300 gold worth of stats into it for a 2.9K price tag, but rather put 700 or 800 gold worth of stats into it to give it a 3.3-3.4K price tag.

It could look something like

Buildpath: + + + +300 gold (Total 3400 gold) Stats: 600HP, 80 Armour (Gold Value: 3202 gold, 94.2% efficient) Unique Passive: AS reduction Unique Active: Randuin's

An item like this could both fill something that's missing from tank's build path options and give Randuin's a very clear niche, which is something that it's PBE variation is seriously lacking.