I've noticed that you are trying to make tanks much tankier in team fights but less oppressive in 1v1, especially (or incidentally) against heavy crit users (skirmishers for instance) who should ideally be doing a lot of damage to tanks. I believe you said part of that isn't so much that tanks shouldn't be able to win any duels against crit carries, its just that the crits have to hit obscenely hard to smash through the tank's resists and health, especially if they have to compete in damage against penetration oriented carries.
So it makes sense to see a combination of nerfs to penetration and a reorientation of tanks towards durability in group fights and less durability in solo fights.
However, frozen heart and randuins omen both stack. It works out to 0.8 * 0.85 = 0.68. That means that just the passives on these items can work together to allow a tank to ignore about a third of the damage output of a crit based auto attacker. This means it takes 50% longer for a pure auto attacker to kill such a tank, regardless of whether it is in a group fight or a solo fight. Nerfing the resists or health of tanks makes them squisher both against armor penetration oriented attackers and against crit oriented attackers.
In fact I see a lot of people building randuins who shouldn't even be building it (yasuo for instance), simply because it is too effective versus auto attackers in all circumstances. If you want to know why armor pen oriented builds seem to be virtually as good against tanks as crit oriented builds, consider that a third of all the attack speed the crit user builds will be ignored by the tank, but none of the armor penetration will be ignored.
Normally this would be a moot point because the attack speed slows also reduces the attack speed of the armor pen oriented carry, but it isn't-- it doesn't reduce the ability damage of said carry or change the run and gun damage. Jhin was so strong without a ton of attack speed because you overestimated the time marksmen would spend issuing auto attacks at full speed and underestimated the amount of time marksmen would spend moving around and issuing pot-shots at frequency that makes attack speed irrelevant. This is the same reason armor pen oriented carries scale at least as well, if not better than crit oriented carries.
Theoretically the shard items should give crit oriented users an edge here-- but they can't. Even the buffs to the shard items on PBE right now won't be enough, and can't be enough without making them too strong. The issue isn't crit itemization, its the attack speed slows. The plain fact is that even if you had a chance to sit in one place and attack at full speed, your damage output against the targets you will most likely be able to do that against is reduced by a third-- thats just too damn much. Its no wonder people feel armor pen orientation is more effective than "auto attacks per second" orientation. People have correctly identified that putting their money on making their abilities harder hitting via armor pen is more effective than putting their money into something that they will be punished for using-- their attack speed.
You need to think about whether passive attack speed slows are really something that a tank item should have. It would make more sense to have tanks ignore a % of ability damage, rather than a % of attack speed, considering the fact that RIOT has repeatedly expressed concern that ability users like assassins and burst mages continue to deal more damage to tanks than RIOT believes is warranted.