Yes, tank items are designed for them because they are designed to buy tank items. This has been true since the beginning of time and only changed when Riot started to jank with the items. Tryndamere is indeed designed around crit and crit is an intended stat for him to use; this only changed when Riot began altering the stat without him in consideration. Crit was not a stat only marksmen bought until Riot removed it from items like Ghostblade or took out of the game entirely (Atma's, SoTD).
Juggernauts do not force you to send multiple to deal with them unless you can't duel them. Even then most of them have very obvious counterplay of either avoiding delayed skillshots or kiting them, either until their buffs wear out or getting them off of their buff zones. They pretty much universally struggle into skirmishers and they have plenty of harder matchups into divers as well. Considering out-of-lane interactions control/waveclear mages are an easy counterpick against pretty much all of them from the mid lane. The only time you can't handle them 1on1 is if you've fed them, you don't understand their counterplay, or if you're a champion they're intended to counter -- which is mainly tanks.
But when Darius, Garen, or Illaoi (who do have both higher innate defense, and the very high in-kit healing that you seem to not count as defense) build Trinity Force
Trinity Force is not an 'offensive' item for these champions to buy. They still fit into the wide bruiser umbrella and have kits that clearly let them apply it to good effect. Why you would say this is abuse of an item is beyond me. Why is my comparison for divers not suitable? They've abused items from both ends when they are intended to be their 'own' class.
who do have both higher innate defense
Negligible base stat differences in the very late game are not what I would call higher innate defense in any way that matters. Comparing to recent Divers who I consider the standard other Divers will be updated and designed around, a Juggernaut being able to heal decently if they play well or the enemy plays sloppily does not measure up to getting to completely ignore all damage from beyond a circular radius, an on-demand damage reduction, untargetability, adaptive shielding, etc. Even older Divers have generous shielding like J4, who I would consider to be a very durable champion. Most means of Diver survival can not be easily reduced by debuffs like Grievous Wounds, and any healing they DO have is generally not their only way to stay alive, AND they're usually on-demand compared to someone like Illaoi having conditional healing or Trundle having conditional durability on his R, because it's based off the stats of whoever he ults.
The juggernauts you've listed don't out-survive these champions except for Garen, and he needs that because he lacks the killing power the other two have while lacking the escape potential of more mobile fighters. Again, if you wanted to make this comparison you should not be using Darius or Illaoi for it. Udyr, or Urgot, or even Mundo's absurd healing would make better cases for it. Divers still have very generous innate defenses and this is part of the problem with Sterak's being rebalanced for them to want to buy it. Many divers can have the durability of a juggernaut now, which is admittedly not much in season 9 but still "enough," then juggernauts lose their main advantage which is having superior defensive itemization.
Shyvana is officially listed as a Juggernaut by Riot and has been since season 5. I don't know what you're accusing me of; I'm using Riot's official classification for her.
mains say that he should be able to outduel anyone, and other half say he is supposed to be a teamfighting monster carry.
into defense.