Here's the problem with **Ability Power** + **Durability** briefly summarized:
>**Goal:** A durable AP damage threat.
>* **Good AP Ratios:** The character ends up too viable as a burst damage threat, and builds straight AP.
>* **Weak AP Ratios:** The character ends up too weak as a damage threat, and builds tank.
>* **Health and AP Ratios:** The character can abuse tank items and items like **Rod of Ages**. Also, relatively few durability-focused AP/Health items exist, limiting item choices that feel good.
>* **High Base Damages:** The character is ends up with too much innate damage, and builds mostly tank.
>* **Creating AP + Durability items:** The items need low Ability Power to not be exploited by Mages and Assassins, resulting in a need for high AP ratios and the issues those entail.
In short, the fact that AP ratios are often found on Tanks, Assassins, and Mages makes it difficult to design items that are fair for durable damage AP champions, and makes it difficult to design AP items that may be more appealing to tank users.
One of the reasons AD itemization is healthy is that AD is a complex stat. We have base AD, bonus AD, and total AD, and additionally our spells and attacks can scale on attack speed, critical strike chance, and cooldown reduction. This allows for items to be specifically targeted, and kits designed to tweak a champion's base AD, base attack speed, and base or bonus AD ratios.
Ability Power champions, meanwhile, have just Ability Power and cooldown reduction. This means we can *only* tweak cooldown and AP ratios. As a result tank and bruisers have to have their ratios designed around the possibility of building straight AP, and items have to be prepared for Mages and Assassins to look to buy them.
Which brings me to the main proposal: **Base Ability Power**.
**Base Ability Power** would be a base number between 0 and some to-be-determined upper limit, scaling up based on champion level. It would impact the damage of spells that scale on **total ability power** or **base ability power**, but not spells that scale on **bonus ability power**.
What this lets us do is design items that care about **base ability power**. Look at the following proposal:
>**AP Bruiser Item**
* +400 HP
> * +30 Armor
>* +50% Base Ability Power
A mage with 0 base ability power and, say, +36 base AP over 18 levels doesn't want this item: it only gives 18 base AP at level 18, and her spells may use total AP or even mostly bonus AP. But to your AP Bruiser who has 40 base ability power at level 1 and gains an additional 80 over 18 levels this item offers 60 base ability power at level 18, which is very appealing.
You could then tailor said character's ratios to prefer base ability power to bonus ability power, which would decrease the appeal of items like Deathcap, Luden's, et al.
#Questions / Answers
>**How would this impact Mages & Assassins?**
Not at all, if you didn't want it to. Base AP wouldn't necessarily need to be a stat for every character, or, if you wanted *some* level-based scaling, you could give a token amount of base AP over 18 levels, making base AP itemization a poor choice for those characters for the majority of the game.
>**How would this impact tanks?**
You'd definitely need to re-balance tanks with existing AP ratios, as most of them are probably better candidates for Base AP ratios and that should be considered on a case-by-case basis.
>**What if we want a character with options for both bruiser and burst builds?**
You still have it! Such a character could have a slightly lower base AP and use Total AP ratios, allowing them to choose to go pure offense or sacrifice some offense for more defensive itemizations.