I don't understand why people say "iPad is just a big iPhone" as a negative. The iPhone is a very capable computer except that its screen is small, which the iPad addresses. So when they say it's a big iPhone, they are mostly correct, but that's a good thing.
People who say "the iPad is just a toy" seem to not like following up with specific criticisms. Those few who do specify seem to call out features that don't fundamentally transform the device, they just make it easier to do what the iPad already does. So if it's a toy, with those requests it's just a better toy.
I'm not saying iOS on iPad is perfect. It could use enhancements all over the place. But it's not as fundamentally far from productivity as people lament. And of course I'm talking about mainstream use cases. The main issue here is app developers. The onus is on them to add full functionality to their apps, and to utilize Apple's platform.