High nit count is fine, but really only useful in bright sunlight. My on-camera monitors are 2200 nits, which is referred to as “daylight-viewable”, because that’s really the use case… direct sunlight. If I’m not in direct sunlight, 250-300 nits is more than bright enough (for me).
Weirdly, the new iPad Pro only pushes max brightness on HDR videos. In all other applications, it’s the same brightness as the previous model (which I own). I’d bet they’re capping it to preserve battery power, but it’s a huge restriction on the usefulness of the new “brighter” screen.