Look, I get it. It's a stat-stick. You buy it and then you get a whole bunch of stats. But there's the problem with those stats. It's a battlemage item, but it doesn't give battlemages their most beloved stat: CDR.
Rod of Ages gives HP, Mana, and AP. Battlemages are bulky spellcasters focused on DPS and outputting consistent damage and control during a teamfight. Theoretically, it's a match made in heaven.
The problem is that HP by itself isn't a very powerful stat. It's easily burned through by enemy carries. If you want to be bulky, you also need armor. And it turns out that even if you have high ratios, 100 AP usually only gives you an extra 20-30 DPS (and if you're getting any more DPS, you want AP faster than that). AD DPS champions, and even those with burst, have the benefit of converting AD directly into DPS. Anything you buy gets added onto your DPS directly. This means it feels *incredible* to buy 40 AD, because you immediately add 60 DPS, no mana cost, right away.
So let's say we want battlemages to get their item and begin scaling really hard with their stat-stick of Getting Everything. 100 AP is actually kind of low-yield on the DPS front, but why? It's because battlemages actually scale off of casting lots of spells.
The champions who build RoA the most are: Aurelion Sol, Anivia, Swain, Twisted Fate, and Ryze. All of these champs cast a lot of spells and use a lot of mana, and like to be immersed in combat. They get a lot of value out of the Eternity passive. But the stat that helps them the most is actually *not* AP. It's CDR! With more CDR, they can trigger the Eternity passive's health regen more often. It also increases their DPS. If you use Swain as an example, you can see that at max rank, the DPS of his abilities is:
Q: 129.6 + .384 AP
W: 16.67 + .038 AP
E: 27.78 + .056 AP
R1: 65 + .142 AP (R2 is negligible)
As you can see, gaining 100 AP increases Swain's DPS by 62. With 10% cooldown reduction, Swain's DPS becomes:
Q: 144 + .427 AP
W: 18.52 + .043 AP
E: 30.86 + .062 AP
R1: 65 + .142 AP
Swain's base DPS is 239, so gaining 10% CDR actually increases Swain's DPS by 19.38 with no AP. To reach parity with 100 AP and 0% CDR, Swain only needs 63 AP. This is not even getting into the many QoL situations where a slightly reduced cooldown on Swain's main damage ability makes him more competitive with midgame right-clickers. That .25 seconds is not a joke!
The sticky thing is, of course, that artillery and burst mages would also benefit from a Roa that gives CDR. Personally, though, I believe CDR is a dps stat, not just a general mage stat. I don't think mages like Xerath and Brand would pick up a roa when they could be grabbing a Luden's for a faster and more consistent spike, unless they wanted to sacrifice DPS for survivability against assassins like Zed. And even then, I'm not sure it's so bad to have Roa be a less terrible pick for mages under threat who just need to survive lane and scale up.
Proposed Rod of Ages:
Rod of Ages (2700: Catalyst of Aeons (1100) + Fiendish Codex (900) + 700)
60 Ability Power
UNIQUE: 10% Cooldown Reduction
UNIQUE Passive - Eternity: Restore Mana equal to 15% of the damage taken from champions. Restore health equal to 20% of mana spent, up to 25 health per cast, while toggle abilities can heal for up to 25 per second. (Please also consider buffing the health regen number to 50 per cast, or having the percentages of health and mana regen increase over time to a higher final result from a lower initial value.)
Passive: This item gains 20 health, 10 mana, ~~4~~ **2** ability power, and 1% cooldown reduction every minute, up to 10 times, for a maximum of 200 health, 100 mana, 20 ability power, and 10% cooldown reduction.
Let me know what you think in the comments. :)