Chips are the enabler to all sorts of critical features and user experiences. Its not just the chip - hardware architecture and software are there too, but three examples:

- maintaining device responsiveness for more and more complex software and higher resolution displays

- 120fps UI (iPad Pro)

- 4k60 video

Re:4k60, try to find another device besides the iPhone that can shoot 4k60 that isn't professional equipment. Best you have is the new Samsung S9 which can do so for a whopping 5 minutes. That's primarily the chip.

It used to be, now most phones (except for some bad ones, mainly on the low cost portion) have mostly satisfying performances.

Sure, all of them drop a frame or two here and there and that's very annoying when you work on graphics, but nothing essential.

IF we could push the SOCs to have at least one week of battery life, that would be pretty awesome, but that's not going to happen any time soon.

They used to be critical features, but I just don't think the incremental improvements are as noticeable anymore. My iPhone 6s feels quite snappy yet.

The iPhone 3G to the 3Gs was an amazing leap in usability though. Everything just worked so much better, mostly just due to faster chips as far as I'm aware.

Yes. Apple’s chips have enabled amazing performance (far above Android on a single core) and very low power draw, letting them get buy with less battery/heat output for equivalent performance.

The 508 in my Nexus 5X is not quite quick enough to be smooth all the time so I can definitely see an improvement jumping to a more modern SOC. But the improvements have slowed down as mobile hit the same sort of limits that desktop had already exposed and now it is on for the same very slow progression of improvement.