The text on the right is absolutely much clearer to read and it’s immediately obvious so I’m really baffled by this view.

I’m not a typographer or designer, but I do care about usability and it absolutely makes a differerence to legibility.

Perhaps it’s because my own eyesight is so poor (with strong corrective lenses, to the point where there is always some inevitable distortion) that I can appreciate it.

Fonts flashing on load is indeed a bad user experience and hard to control —while the CSS controls for it are well documented, it’s still dynamically determined and if it happens ultimately depends on how long a font takes to serve, making the best defence against it when using a web font keeping them small and using a good CDN.