I actually found a decent workaround for this on elementary OS. It turns out you can manually specify a 3000×2000 resolution and a 1500×1000 resolution for when connected to external displays.
You are still effectively getting 1.5× scaling and the slight bluriness that implies, but it’s the least-bad solution I’ve found on this hardware. Better in my experience than the experimental non-integer scaling in GNOME on Ubuntu, which caused screen tearing and weirdly-sized window decorations.