Comparing my roommate's 2XL screen vs my 3XL, his is more dull. It's overall sharpness is not as nice as the 3XL. They also have display settings for adaptive, boosted, and natural color modes on the 3 XL which let's you change how the screen shows off colors. Overall the screen on mine makes up for the ugly notch. It's just much more crisp than it ever was on my 2XL.
I concur. Even though I no longer have my Pixel 2 XL (it's already been sent to Google for the trade in), I did have time to compare the screen to the Pixel 3 XL and I can honestly say that was the largest improvement by far. Second largest would be the speaker loudness and clarity.
Have you watched any HDR videos on your Pixel 3 XL yet? They look phenomenal!