Outdoor visibility (max brightness)

Everything vs. my s9 has been a big upgrade except wireless charging (meh) and this (Absolutely awful, massive downgrade)

Considering I largely bought it for a better experience with Pokemon Go and Ingress, not noticing the poor brightness was a bit of a mistake... on a nice day it's barely usable...

Gonna confirm what @Cloudane said.

Outdoor visibility sucks compared to my previous phone (s8), but I hope because lower brightness it won't get burn in like s8 did.

It does have the benefits of lower screen burn risk and longer outdoor battery life admittedly so it's not all bad, just a bit of a shock coming from an s9. I also don't think the factory screen protector helps, it's relatively opaque (you can tell at the edges) and causes a lot of glare. I'm wondering if the bare screen has an anti reflective coating but have a glass protector on the way which should at least improve it.

Same here. It's noticeable downgrade in outdoor visibility for me coming from Samsung Galaxy S7. It's still usable but my S7 was just better outdoor.

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.