Well, it is somewhat on iOS because somehow Apple's software gets extremely heavy. Wirth's law or something. The iPad 2 used to feel pretty damn speedy, now it's an absolute dog.
Hopefully that won't actually happen. Apple and Google are putting a great deal of thought into the APIs and features they're implementing on iOS and Android with much consideration to factors such as battery use and performance.
That being said, the latest versions of Google's apps have really kneecapped the Nexus 4 which I've used as my daily driver since 2012. Sadly I might just have to upgrade.