Here's a small demo with the bare minimum (open link on an iOS device, it's a debug view link): https://codepen.io/linkus/pen/gOojdxR
On iOS (both safari and chrome) the scroll fps drops down massively while touching the screen. Once I stop touching (after flicking) it's smooth.
Also, on iOS safari the browser bars show/hide, while on iOS chrome they don't (which is the expected behavior). Also, on iOS safari it sometimes starts jumping while in mid-scroll.
And another interesting thing, even though the documentation states that there's no smoothing of the native scroll, it still doesn't look like native scroll, as it scrolls faster than my finger.
I've been using ? ASScroll up until now, which works 100% perfectly on all devices, it never shows/hides the url bars on any browsers, doesn't lag while touch-scrolling, always perfectly reports the scroll positions and it relies on native scroll on touch devices (all of which I wish ScrollSmoother would do too).