So how were mages nerfed exactly?

{quoted}

No we have more mana regen than before.

I don't understand what you're not understanding. Doran's ring used to give 50% additional base mana regen. That is no longer the case. Doran's ring used to give 4 mana upon killing a minion. That is no longer the case. They increased the base mana regen of each mage slightly to compensate for the way they gutted Doran's ring's mana regen. But ultimately it is less mana regen. Even with the slight buff made to the base mana regen, it doesn't compensate for the mana regen lost with Doran's Ring. If you're a mage that didn't first buy Doran's, you weren't really effected. But there are few that don't start Doran's Ring. Also, mana based items got nerfed. Lost Chapter got nerfed with the additional 200 gold cost (as I already stated.) This nerfs champs who rush that item because they have to stay in lane longer to first back buy it, or buy half first then half after. They did increase the amount of AP to compensate for it being more expensive, though. Still, it wasn't bought for the AP, it was bought for it's passive ability. If you buy it too late, the passive ability is useless. Not to mention that every mage got their mana growth cut in half. Why is this important? Because you run out of mana faster in later game. So let's take Ahri, for instance. At first level, she started out with 334 mana (pre nerf), with no items. At max level she would have 1184 mana with no items. Now she starts out with 418 and at max level she has 833 with no items. That's over 300 less mana at that point. Again, it's not a super huge nerf. But a nerf none-the-less. They wanted champs to focus more on their mana pool. They also wanted mid laners to focus more on poking the enemy champion rather than just farming.