I have to say, both machines are terrible. X1 is pretty slow (some 4c i7 with basic iGPU) - running dual 4k displays, webex and similar apps is pretty slow, even scrolling websites is not smooth quite often. Also, fan never turns off and battery life is well, not great.
P15 is just ridiculous for it's MSRP, touchpad is shit, battery life is shit, CPU sometimes gets stuck at ~400Mhz just because (x1 also has this problem actually) and after googling it seems to be common issue with lenovo hardware (WTF)
Also, why they they included 2 thunderbolt ports and 1 usb-c where not one of them supports charging is beyong me, having to use this stupid lenovo psu every time is PITA)