Not exactly your experience, but using a single (non-4k) external monitor is slightly painful for me with my MBP. It sometimes takes ~10 seconds for my display to work after plugging it in, with lots of intermittent flickering as the OS "figures it out". And afterwards, the menu bar on the external is a bit glitchy looking on the right side until I click on it. With my other laptop running Fedora the experience is much faster/cleaner.
Not a big deal, but just thought I'd mention that macOS isn't exactly perfect when it comes to external monitors.
Apple introduced some issues in recent generations of hardware that I haven't heard many people talk about. A recent Macbook and Macbook Pro with USB-C using an Apple's USB-C to HDMI adapter had terrible connection issues for me. I did hear a few references online from others with the same issue. Using a 2009 and 2011 Thunderbolt to HDMI the same monitor worked fine.
I fixed the issue by using a USB-C to DisplayPort adapter made by a third party. I think that also allowed 4k at 60Hz. I later switched to a multi-port adapter with HDMI out and didn't have this problem.
This problem was horrible noise and loss of connection. People hate dongles for the convenience and price factor, but I think everyone underestimates how it introduces technical and compatibility issues.
Not a big deal, but just thought I'd mention that macOS isn't exactly perfect when it comes to external monitors.