This accusation seriously has to stop. They're constantly pushing performance improvements (most recently they've made their PDF viewer more efficient and found some efficiencies with images), they push millions of lines of new code every year on a rapid release cycle with an extremely rapid release cadence throughout the year in the release notes for every updated version go deep on the weeds for everything from CSS fixes to performance improvements to bug fixes and so on.
I at least understand the accusation that a bunch of their side projects didn't end up contributing to their bottom line and may have hurt user experience, but the velocity and volume of code they're pushing is not debatable. and the vast majority of it is exactly these kinds of improvements in technical fixes that people in the HN comment sections keep claiming aren't happening.
I'm not going to say everyone should read the release notes, but you definitely should if you're comfortable accusing them of not actually working on the code.