"significant" is the key word here. I'd be hard pressed to think of a generational release of an existing phone line in the last 5 years that I would describe as a "significant" improvement.

The things you listed (camera and chip speed) are basically the only things left that these companies can claim is better than last year's model, but only because it's so easy to use synthetic benchmarks and numbers that mean nothing to make them sound like a dramatic improvement despite the fact that we've reached the bottom of the barrel in terms of diminishing returns on the user experience for smartphones in their current form. More megapixels don't matter anymore, CPUs are hardly a limiting factor and yearly gains on their performance are marginal at best, and we have more than enough RAM for pretty much all use cases.

My point is that if these companies insist on re-releasing the same phone every time, maybe they could space it out a little.