Maw vs. Zhonya's

Maw is the go-to defensive items for AD champions when facing AP, and Zhonya's is the go-to defensive item for AP champions against AD/assassins. I understand that AD champions need a little extra because they are melee for the most part and they need to be able to get on their AP mage targets, but in my opinion the difference in power level between Maw and Zhonya's is much too high. In lane, lets say for example a Zed and a Brand are going at it. The Brand is essentially forced to rush a Seeker's, but the Zed can go either Serrated Dirk or Hexdrinker, both of which are much more powerful options than the Seeker's. Lethality cuts through armor better than magic pen cuts through MR in the early game and hexdrinker essentially guarantees that the AD champion wins the 1 v 1, unless his opponent is ungodly fed, whereas Seekers just gives you a better chance. Also, lets say the Zed builds a serrated dirk, then goes into a full maw, then finishes duskblade afterwards. He sacrifices little to no damage during this process while gaining incredible amounts of durability, whereas if the Brand goes Lost Chapter into Zhonya's into Nomicon, 1. he's likely to die before he gets enough armor 2. seeker's doesn't provide nearly as much durability as hexdrinker, and 3. he sacrifices a siginificant amount of early damage. It just seems to me that in the case of Maw and Zhonya's, the power level disproportionally favors AD champions. I am aware that AD champions do need an advantage in this area, but whether or not they need this much of an advantage, I seriously doubt.