All an H9 Max is an H9 with all existing algorithms pre loaded and any new ones free.
Why would they use a new processor to do the exact same job?
Availability. While I could be wrong about Eventides business reason for discontinuing the H9 and H9 Core, if you can't get the processor, you can't get it.
If you assumption is that Eventide wouldn't want to make a new revision with the same sonic characteristics of the old one, then I think you are incorrect. Once you have enough processing, more doesn't give you a better sound. It DOES let you use a more powerful algorithm and a more powerful algorithm could sound better.... but not always.
VST plug-ins are a good example. Does a specific VST plug-in sound better in a faster PC? Nope.
Without seeing the chips inside the H9 Max, I can't really know for sure, but this statement:
" In addition, due to supply chain disruptions and component shortages exacerbated by the COVID pandemic, we will no longer produce the standard H9 and H9 Core after 2020. "
It certainly sounds like a supply issue.
I believe that the KPA2 will be the same. The algorithms for the amp, cab, and the latest efx are already industry leading. Faster processing isn't going to make them too much better (insignificant IMO). I believe the KPA2 will be more about additional features, and greater capability.
Also, your assumption that an H9 Max is just an H9 with all existing algorithms preloaded is likely incorrect. If that were the case, they could have offered a paid firmware update and achieved a higher profit margin on the sale. Show me an image of the two inside and I can tell for sure.