> "...most of my Pi 4-based projects seem to idle around 3-5W."

Some current Intel NUC models can manage less than 5W idle power as well, e.g. https://www.anandtech.com/show/15571/intel-nuc10i7fnh-frost-... but don't have the limitations of the Pi.

Have newer versions of these things improved? Our company bought a new round of NUC7s and NUC5s and life span was pretty abysmal.

I still use a NUC5i3RYH every day. It has been remarkably stable, haven't had to replace a single part or have any issues since building it in 2015, and makes an outstanding Hackintosh to boot.

Either I got lucky with the two I own, or your environment was to harsh for them?