Tanks Rework should come after the ADC rework
title
They are just non-existent champions right now except tahm kench. Their items are useless now, and they all have been nerfed into oblivion (
) there are no reasons to pick them over juggernaut or
Riot needs to do it, do mini reworks to every tanks to achieve a global goal like they did with juggernaut (immobile high tankiness high damage champions).
Tanks should be champions that does high damage in early game while falling off, and help their team in late game with high utility. Their tankiness should scale in the game and not just be tanky early/mid game if they snowballed while being a piece of paper after 30 min in the game. And that's riot's big mistake because they either tend to be unkillable if they are 15 kills ahead or can't do their job effectively.
How to fixe it? fixe
first, without them being abused by everybody. In the same way they buffed warmog without anyone being able to build it like in 2013
give to those items bonus effect if the champion has more than X armor (200?) that way it isn't 100% useless to stack resistance and it also fixes bruisers or some kind of champions abusing items like frozen heart for its cheap cost.
should allow you to bring more utility
aura radius 700 --->450
new effect: grants heart of frost if you have at least X armor heart of frost: dealing damage to a unit slows its attack speed by 15(+0.5% every 30 armor) for 2 seconds, stacks with the aura (10 seconds cooldown)
should makes you tankier later in the game
cost: 2200 ----> 2500
armor: 100 ----> 90 new effect: if you have at least X armor, grants empowered armor empowered armor: reduce the damage dealt by auto attacks by 15% and reflect 15%(+25% of your armor) damage
_Riot nerfed it because sometime people rushed it for few gold and until having proper counter (magic resistance, lifesteal, armor pene) people were discouraged to attack them. Now with those changes, Thornmail scales well into the game while being weaker before. _
cost: 2600 ---> 2400
+
+
+
+ 600 gold
cost:
health: 450 -----> 350
armor: 45 -----> 35
magic resistance: 0 ----> 35
passive: damage changed to 35 all levels
changed the build path
_Tanks should do high damage in early/mid game and that's what sunfire should do while falling off later in the game due to its stats, it should also give them the possibility to wave clear. The magic resistance here is to give the possibility to tanks to build it in order to do damage without fearing the problem of facing magic damage champions
_
costs: 2700 ---> 3000
health : 400 ---> 600
armor: ~~60 ~~ ---> 70
passive: changed the duration from 4 seconds to 1 seconds for each 100 armor/100 magic resistance

cost: 2600 ----> 2900 health: 300 ----> 450 cooldown reduction: 10% ---->20% duration : changed to 1.5 seconds (+ 1 seconds every 100 armor/magic resistance)
every items were changed so they scale harder in the game while also bring amazing utility to the team and that's why the cost was increased to change tanks from snowballing low cost items to like everybody: high cost items that gives more benefits in stats and utility.
Now let's move to champions:

now has 1.25 mr/lvl sap magic: now trigers on spells arcan smash: mana cost changed to 65/60/55/50/45 from 45 all ranks slow duration increased to 2 seconds AP ratio reduced from 0.4 to 0.3
vengefull maelstrom: now grants bonus ms to all friendly (and maokai) units in 475 range (aoe of the ulty).
changes to make him working as intended: he should scale less later in the game while bringing more utility and tankiness later in the game. The mana cost change is here to make him less obnoxious in laning phase.

puncturing taunt: cooldown changed to 12/11.5/11/10.5/10 seconds shred duration changed to 3 seconds all ranks

Glory in death: 100% lifesteal -----> 10% of max hp heal
soul furnance: delay reduced from 3 seconds to 2.25 seconds
roar of the slayer: base slow increased from 20% to 70%
duration changed to 1.25 seconds increased to 2 seconds if sions hits a creep
unstoppable onslaught: max ms increased
the shield change is just a logical change, right now sion can never triger his shield and 3 seconds is too much, but i played sion before and 2 seconds was broken, we need to find a duration between 2 and 3. this passive change makes it so he isn't punished by gaining hp while not gaining AD. Finally the maximum ms of his ulti is increased to give him the possibility of hitting someone if he used his ulti at max range

ground slam: damage changed to 80/120/160/200/240(+20% armor) from 60/100/140/180/220(20% AP)(+30% armor).
    already work well
now i have no idea because i never played this champion, please post your idea to improve her
and maybe 1 item that is different depending on the mage..
Sense the new rift...
4 new items for tanks.. Mages gave up DFG for their new item Echo...

that gives me AP and something to help my team...
and maybe...
but it's cost now went up with the Buff to it.. I used to build it as a support item for taking down towers as a mage support and a adc who may be able to take it quickly..
Could build this..
gives 100 AP now just like luden mages's item are a lot more than you are saying, didn't even talk about liandry