The corrections may not amount to much, but there is no reason to believe that his version would be a failed experiment like the Apple III or the Lisa would have taken it's place.

Part of the magic of the Macintosh was the simplicity of the hardware. In that respect, it was much closer to the Apple II than the Apple III or Lisa. Consumers may not think much about what's inside the case, but it matters when it comes to manufacturing costs and that translates into the cost for consumers. While the original Macintosh was by no means cheap, it was about half the cost of the Apple III and a quarter of the cost of the Lisa. Heck, even the adoption of the Macintosh was slow because of its price. Maybe a less expensive 6809 based Macintosh would have had more success in the market, at least early on. It's also too easy to read too much into the failure of the Canon Cat. The Canon Cat was introduced years later. User expectations were starting to solidify around the GUI at that point. (Then again, success was not guaranteed. Lacking compatibility with the Apple II would have held it back. Especially so after the introduction of the IBM PC since the IBM PC had IBM backing it.)

I also think the adoption of the GUI for consumer computers would have been delayed considerably without the Macintosh 128k. Early machines that supported a GUI tended to be expensive. Early versions of Windows were crude. The only real outliers in that respect were the Atari and the Amiga. Would they have supported a GUI without Apple taking that first step? It's hard to tell.