We need a defense rework asap and here is why
Medium sized all of text incoming do not fear there is tldr
I have seen threads about how damage needs a nerf but in all honesty i don't think damage needs nerfing. Nerfing all damage would be one hell of a balance nightmare to do. The way champions deal damage and how much would be apropriate can be slowly rebalanced and reworked with class updates, there will always be outliers in classes which can be put into certain sublasses like juggernauts for example they funtion differently then say a xin zhoa who is also a fighter.
Defense is just ineffective right now and doesn't work properly which is where i see alot of grief coming from
If a tank snowballs they can feel unkillable due to them stacking defense and you not having the tools to cut through it. But once you do have those tools like armorpen or magicpen you can suddenly cut through them like butter. This is especially true for dps as high health alone would be enough to defend vs burst its not effective vs dps this is where you need the defenses but as they get penetrated all you have is health which as i stated is ineffective.
So we need a way to make defense power more appropriate
Now Riot has already done something which seems like a very reasonable solution at one point, they differentiated between base armor and bonus armor, base health and bonus health what we now need is base magic resist and bonus magic resist as this will help with some magic dps problems which sometimes Aryze cough
cough 
My point being, i dont think penetration should always be super effective, but rather should be appropriate.
For example Darius has a high base armor of 97 if im not mistaken, this means he will always have at roughly 50% damage reduction vs AD unless shred or flat penetration is involved Vs adc he feels adequately tanky you dont just blow him up, but thats also because he can heal alot. But even with mortal reminder you cant just kill him with a few auto's as an adc which feels about right in combination with his healing power.
This where i want to make a change currently you see black cleavers everywhere which is fine but it shreds total armor making it effective vs everyone Imho i think it should be reworked to shred bonus armor
The same thing goes for magic penetration voidstaff should work vs bonus magic resist, and if there ever will be a magic resist shred item it should also only affect bonus resist, this will help out magic dps
The only thing which should really be effective vs base armor/mr is flat penetration
This will allow for tanks, and other tanky sublasses like juggernaust, to be given high base defense which means they will have at least a certain base level of tankiness.
This will also give more and so much better balancing levers
think about it, if tanks were to get the highest base armor in the game and items which give shred and pen will give low or lowish AD. And AD assassins were given good AD scalings but low scaling base damage then they would almost certainly not want to abuse %penetration or shredding because those would be less effective on them then flat penetration this will amke a tank with high base armor and alot of bonus armor a tough opponent but a squishy with low base armor a proper target for them.
But thats just one example of how this could be used balance wise, Let us look at another one. Deadmans plate was primarily a juggernaut item for champions like Darius and volibear to get into the middle of fights more easily, then it got picked up by everyone to the point where i have seen it on a Fizz, a Veigar an Azir a master Yi. None of them are juggernauts or beefy dudes who want to be in the center of a fight and were faciing a bit of trouble getting there vs some opponents thus eneding the item. An item like this could be given 50% of base armor making it stat wise excellent for juggernauts and tanks but alot less effective on other classes thus preventing abuse for the mobility it provided. Ofc % of base armor should not be used liberally because off meta builds etc do have a place just an extra tool to prevent abuse where its apropriate
The only place where i can see total penetration or shredding apropriate is in a champions kit because a cost can be attached like cooldown and mana or energy.
Now lets talk about health
We already ahve a bonus & base health thing, but i hardly see this used for % damage Very often you see %max health damage % current health damage or % missing health damage % damage could also be subject to bonus vs base health
This doesnt mean we have to change how all % damage works by reworking all the abilitiess and items But tanks could have acces to an item which makes % health damage only target their base or bonus health This would need certain limitations to prevent abuse cases, something like a warmogs hearth requirement seems about right.
TLD;DR Maybe not all of the above is perfect but i do think tankyness in generall could use a bit of an overhaul because sometimes it really feels like you melt as fast as a squishy when playing a tank.
It just doesnt really feel like you can be tanky anymore and i do not think doing a total overhaul of damage is feasible but given that we can differntiate between bonus and base resistances/health we can utilize this to make the counters to said stats feel more appropriate aswell as to give tanky champions at least a certain basic effecitveness at absorbing damage

Maybe
and
if Riot ever got around to the tank update.
would have to spend extra money on a mix of both.
MR Shred Item
