Having all scrolling be consistent feels good once you get used to it.
That doesn't necessarily mean it was a good idea for Google's hosted AMP pages to use overflow scroll all along. The inconsistency definitely did feel weird. And the way they do scrolling prevents Safari from auto-hiding its top and bottom bars. I believe all the desired scroll effects could have been achieved without the use of overflow scroll.
Edited to add: the AMP scrolling model also breaks tapping the top of the screen to scroll to top, and this won't be fixed by scroll rate changes.
It never occurred to me that Safari page is what the outlier, I just assumed that Safari pages matched the rest of the system and iframes for the thing that we're off.
Maybe this won't be as hard to get used to as I feared.