Huh, how is display-p3 supposed to maintain the white point if the different color components have different luminosities than they used to? It seems like red and blue are lighter than they used to be, and green is slightly darker? I guess one way of looking at it is that the original "green" had a little bit more "red" and "blue" in it, and display-p3 pulls those bits out of the "green" and moves them into "red" and "blue", making the red and blue even brighter and the green darker (but more saturated).
srgb
adjusted srgb
adjusted display-p3
display-p3
srgb again
I guess these are the same luminosity but they're different colors!
Just the primary components, mostly red got brighter, and green got darker as a result of losing some "redness":