What's the rationale behind Marzipan causing an exodus of pro users? Even if there were a flood of low-quality mobile apps onto the Mac... I don't see how that would reduce the availability of existing desktop-first apps.
In case of Linux and Windows you can see their effort to improve things. Their failures and shortcomings stem from either decades of legacy (Windows) or lack of overarching vision and resources (Linux).
Whereas MacOS... It has always been billed (and billed itself) as the UI/UX front runner. It was (or was trying to be) polished, consistent, good.
Apple had Human Interface Guidelines in as early as 1987[1]. Apple was the definitive yardstick interfaces would be measured by.
But in the recent year(s)... Apple has been consistently dropping the ball themselves. When their own first-party apps break almost every single HIG [2], how can one expect third-party developers to create quality apps. When their own third-party apps are locked in to landscape mode (iOS dashboard and iOS books interface), how can one expect third-party developers spend any significant amount of time creating seamless experiences across multiple screen sizes (and Apple’s own Marzipan apps like Newsstand and Home are barely ok at best).
When your OS is no better than the competition, what’s to stop people from using the competition (which actually shows willingness to improve).