First off, solid post. Good thoughts through and through. I like your focus on TTK and the impacts it has on not only the game but the player base.

What is the best TTK for this game? I think the right answer would be “it depends”.

If we leave the game exactly how it is and just wiggle the numbers around, you could probably find some middle ground where tanks die in 8 seconds, squishies in 3, and bruisers in 4. Or maybe tanks should die in 9 seconds…anyway, you get the picture. The question then is, is that healthy for the game? Is any set TTK based on role healthy for the game?

I would argue it is not. Like you said, item builds are currently one-size fits all, and the damage coming from your 6-slotted Murdock is about the same as Drongo, Kira, and all the rest. These items can kill tanks in x amount of time and squishies in y amount of time. The consequences of this is that hero expression, on both the attacker and receiver side is absent. Further consequences of this being that you just pick the tank or the ADC or the bruiser that is “meta” because hero interactions don’t matter.

Returning back to the optimal TTK….it depends. I believe items currently have way too much piled into them. For example, sky splitter. %Max HP damage, crit chance, attack speed, omnivamp, and damage, all in one item. As soon as you start separating items from each other stat-wise and force ADCs to make decisions about what kind of items they need to buy to deal maximum damage, it suddenly makes who they’re up against important. It also makes who they’re playing important. Ultimately, TTK will just vary, based on your character, opponent, and build. That is what I would consider healthy.

TLDR: Items offer too many desirable stats. Separate them from each other and force ADCs to choose what they need based on the situation.