I'll use the system zoom if I need to, but it's very awkward compared to the browser zoom. You're stuck panning around the magnified screen with one set of gestures, while also having to scroll through the page using the browser's gestures. It works but it's not pleasant.

The excuse I always hear about disabling zoom has to do with the multi-touch delay. I can somewhat see the sense of that for very particular applications, but definitely not for AMP, which as I understand it is meant for mostly static content (I'm only assuming though).

More often than not, what I find is that if I override zoom disable and then browser zoom on a site that doesn't allow it usually, it ends up breaking the layout as you zoom. This makes me wonder if they're just disabling zoom because they can't be bothered fixing their CSS to deal with it.

But what's wrong with using the web browser's zoom tool? Why is it somehow worse to get reflowing zoom? This idea that I'm using a phone optimised site so all text should be 8pt is just bizarre. It's not like the UA author has removed support for zoom: they're just disabling it arbitrarily.