> 2. If the 4k screen is on your laptop, good luck ever having a decent experience plugging in a 1080p monitor. Also good luck having anyone's random spare monitor be 4k.

I have been running two 1440p displays on a 4K retina MBP and the experience has been impressively seamless. Both with Catalina (the latest) and High Sierra

The biggest problem is with Apple port splitters; they are crap and sometimes monitors wake from sleep with a garbled picture