> You can use it to make the entire phone greyscale, which entirely defeats a huge range of techniques that apps and feeds use to draw your attention

As a counter-anecdata: I've had my phone in greyscale for a few years now. At first it worked amazingly, made me hate my phone and pickups dropped significantly. But over time I realized "Oh wait, 90% of my phone use is text and this is actually super nice for reading".

Now I use my phone just as much as before, except in greyscale.