I think many users scale their 2K/4K displays until they are acceptable, they leave their standard 1080 monitors unscaled. Perhaps you should try that: scale the 2k monitor, and don’t scale the 1080p.
I do the opposite because I want images and documents to preview at the DPI of my 4K monitor - apparently that is quite unusual (discussed here this thread). KDE developers expect that users don’t mind that images or document scales are changed, these users just want a retina effect.