Could you as a developer (Access) have foreseen this in the past? Not really. Now the task at hand to make it compatible with the ARM architecture makes it even more complicated than it was before and boy it would mean a full code overhaul. So I'll go on a limb here and guess that Apple knew what was coming and correctly scheduled it on their last intel branch models and quote 'security' as their main reason, taking away scrutiny from the M1 that would have caused the same issues and even on a lower architectural level.
As for my previous statement about Access not being at fault for Integration part, I stand by it. Also they do their due diligence by making sure the information is available on their site and forum that Mac currently has issues. The one part where I do agree with you, is that their transparency in regards to the future and a possible resolve, are sub-par.
I work for a developer/electronics manufacturer which uses both iOS and MacOS so I have background knowledge of how this works. Apple does release confidential memos notifying developers of upcoming changes in each OS version when they start to appear beta builds for SDK holders. These changes are known well enough in advance so that developers can make necessary changes to maintain compatibility. So that part of your argument is invalid.
Also, I am acquainted with Sean Costello who is the driving force behind Valhalla DSP. He recently posted that it took him a day to re-code one of his plugins for the new M1 platform - https://www.facebook.com/ValhallaDSP/posts/10158708762617226 He's also released M1 compatible builds of his commercial plugs for the new platform as well within a month of the new platform becoming fully available. So this is not the massive code overhaul you are describing, even with the simplistic GUIs he is using in his products.
So from my perspective based on my knowledge of how these situations work, Access/Kemper and Ploytec had MONTHS of advance knowledge of these forthcoming changes with Catalina. The problem I often find is that many developers either wait until the last minute to get their code compatible with new OS releases or don't do it until the new OS version is already released to the Public. Ploytec updated the drivers and passed them on within a reasonable amount of time so the fault for this lapse lies squarely with Access/Kemper.