While I don't necessarily agree with this, I can certainly hold Apple accountable for not informing me that installing the latest OS upgrade would affect performance substantially and thus giving me the opportunity to make an informed decision as to whether or not to install the update. Had I known about this I would never have upgrade as the tablet was already doing everything I needed just fine. The failure to do this was a conscious decision on Apple's part, intended to force me to buy a newer product.
The vast majority of iOS users who upgraded saw no performance hit at all and most saw improvements. . . so there was nothing to "warn" about. A minority of the millions of iPads, apparently yours among them, developed problems with the iOS 8.0 version. I had problems i documented on FR and documented to Apple, but no loss of battery time. Apple quickly released an 8.1 update that addressed most of those problems. 8.1 solved most of the issues I saw. Did you install it? 8.1.2 is intended to catch more.