Original lite is a clean and elegant Lua implementation of text editor with quite a few features. Lite-xl does the last mile to better integrate with OS and does many features that were out of scope of lite, for example multiple cursors. In that sense lite-xl is like you say a bit more complicated, to make it actually useful for everyday tasks.

I use lite embedded in my own application, and lite-xl as a quick and competent note-taking application (with custom plugin to set filename to date + document header). Both are great to me in their own ways.