Thinking about this some more, my guess is that we're talking about very different things. As I said, at 30% with adaptive brightness on, my Pixel 2 is readable in direct sun and (updating) even when the sun is about five minutes away from its highest point in the sky on the day of the summer solstice. That's at a location just barely within the northern subtropical zone. 3dd1 said it's not bright enough at 100% in bright sunlight in the UK.
Those two statements are not necessarily contradictory. When I say it's "readable," I mean just that: the screen can be read, but not necessarily comfortably. The crucial point is that you can read it well enough to adjust screen brightness, if needed. I've had plenty of phones that could not be read well enough to do that in sunlight. (That's why I have a Tasker profile that sets brightness to maximum when I flip the phone over twice rapidly.)
3dd1 did not say the screen isn't readable, just that it's not bright enough. And that's quite possible, even though it's not my experience or my opinion.
