This comes from playing Paladins and how much I absolutely love simplifying the system and making things more stream lined and clear.
League of Legends as a completely useless number when it comes to armour and magic resistance to make the player feel good about themselves with getting that useless number, the number means nothing. What the number indicates is the percentage reduction of that damage type. So why not only have the percentage reduction and skip the crap fluff number that means nothing?
Put it simply we should. We should also remove base armour and magic resistance, we should also remove it from runes. All these numbers do is make it obscure to balance for, but if everything dealt true damage, then damage is a lot more clear and easier to balance for. At least early on everything does true damage.
Now, with only health and the damage the ability and attacks do being indicated, designers and balance team (mainly balance team) can a lot more easily adjust these values and have a significantly easier time balancing the game. Most importantly, it is way easier for the player base to understand their own damage output and what it takes to kill someone, but more importantly is a lot more clear to why you died or not and accurately and consistently know every time someone's damage output.
So with everyone starting out dealing and taking true damage values, there is only that clear value of the damage the enemy can do and your health bar. For the record, I do think base health and health item should be increased, mainly base health, which makes it easier to fine tune balance with larger numbers to deal with so the balance team does not have to use decimal values for damage and instead use whole numbers for everything - lower damage especially a lot easier to tune for with higher health bars with no innate mitigation (outside of champion specific passives and abilities). Main point here was to state that lethality and magic penetration would be removed with other penetration being changed for a new system, all other shreds and penetrations removed and possibly replaced with something else.
# The meat and potatoes are here!
Despite everything starting out as "true damage", there will still be physical and magical damage. This is because armour and magic resistance will be replaced and be item exclusive for the most part (some tank abilities will be changed to be physical and/or magical damage reduction instead to a similar respective power level) where they simply state how much **percentage** physical damage or magical damage the item is mitigating, adding on additionally just like how cooldown reduction works.
Would there potentially be a hard cap like with CDR? Perhaps, mainly since 100% physical/magical damage reduction would make you immune to that damage type, with the exception of true damage forever living up to its name, cannot be mitigated or increased in its damage output. Let's say the cap for physical/magical damage reduction is 75%, not 40/45% like CDR, mainly because there will be the majour penetration items still which will reduce this value by 40% multiplicative (does not subtract 40%) just so there is a way to eventually kill those tanks and actually end the game.
To sum things up.
I honestly think a streamlined system will make the game a lot easier to balance for and help remove fast kill metas like what the game is currently in. If the balance team knows exactly this damage nuke and this critting attack does this much damage with the removal of a billion X factors, then they can probably tune the game and no longer need to make small adjustments every 2 weeks in the patches for a more stable game experience.
The patches will move into a system where they are more grand sweeping changes since you are not constantly play cat-and-mouse with this flawed and finicky damage mitigation system which honestly means nothing right now, it is a complete joke.
Most important aspect, this system of simply having only one set of numbers saying exactly how much damage is mitigated is just clear for every player. Early game, you know how much you do and how much you take. Later game, if you opt into defensive items, you know how much less damage you take and the enemy team can see your items and know why they killed you with this burst combo back then, but now you live with that same burst combo, check the scoreboard and see that you got an item that mitigates 10% magical damage for example.
Paladins does not have a penetration system at all and the item mitigation cap is at 21% for each damage type since you cannot buy anymore of that item, but League of Legends is obviously set up differently and I do think a very similar system could work for League of Legends. Mainly the difference being is that damage is set to the same value, where as League of Legends as ways to increase the power of attacks and abilities, so likewise a more significant damage mitigation system would be needed to off-set this, but I digress.
Let me know what you all think and take care everyone!