It's been touched upon in the various "CPU" threads, but, basically, Kobo Mk.7 devices have hardware that's very, very, very, very close to a PW4. And somewhat close to a KOA2, if you forget the CPU swap, which wouldn't have the same impact on the Kobo software that it has on Kindle.
(TL;DR: Kobo used to be half a generation to a generation behind Kindle, but they've started to catch up, so I definitely do NOT mean "poor hardware" in general when talking about current gen Kobo devices).
The big difference is how that hardware is tied together, as that's done entirely in-house with Amazon via lab126, while the board designs are from NTX on Kobo's side.
And then, of course, the software stack
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You just have to remember that Amazon has the resources to throw rivers of $$ at the issue, something no other current actor can rival.