A little re-evaluation: In fairness, whilst it's not on par with a Samsung screen outdoors, I was using it on some very sunny days at the weekend and it was still adequately usable. Pokemon Go (light background) was easier to see than Ingress Prime (dark background). It was only a problem when angled so that the display is directly facing the sun, a problem that can be solved by moving slightly
Also it seems there's no polarising filter which probably doesn't help matters but there's a positive to that: I was able to wear polarising sunglasses without them 'interfering' as they do on some other phones. I found no difference in visibility with the glasses on or off.
Getting rid of that factory fitted screen protector and installing a glass one also helped a bit. The factory one gets all smudged up.