I recently purchased an iPad Air 2 after only having a Macbook Air and iPhone.
I think one of the major issues with iOS is that people are continuing to expect to, and try to use their tablet PCs and iOS like a desktop computer. Over the years I've become more and more dissatisfied with using a regular computer. Frankly, even with the Macbook Air I feel like I'm tied to a desk, and overloaded with features, and programs.
One of the things I like about iOS in comparison to OSX is that often times iOS apps, especially the Apple versions, present you with a minimum amount of necessary options, and they force you to be much more deliberate and simple in how you interact. For me, it cuts out a lot of the clutter and allows me to really focus on what's important; I like that.
Frankly, software issues aside, I don't really feel like integrating OSX and iOS on the same device is the answer here. I think that you really need to evaluate what you use these devices for, and then go with the one that meets your needs. If you need a desktop OS and desktop features, buy a computer. Don't buy a tablet and then expect to do the same things.
The OP said nothing about integrating OS X and iOS though. He even specifically mentioned not wanting a hybrid OS like the Surface.
He is totally right, though. The iPad is capable of running a much more robust version of iOS 8 than what is offered on the iPhone. It still bugs me to this day that all the iPad home screens are are a stretched out version of the iPhone. Don't get me wrong--I've had every iPad and I love them, but seeing a bunch of icons widely spaced apart still seems like an afterthought to me. The bigger real estate is just begging to have more information displayed on it besides a pile of icons. Sure, I have my cute little "Today widgets" now, but really they aren't as good as a full home screen implementation. There are loads of things that could be enhanced strictly for the iPad platform, but I would just love to see the iPad have its' own unique home page layout. Maybe widgets are where it's at; maybe they aren't. That idea has been tossed around since Android got them--I'm sure Apple could come up with something better if they really set out to do it.