I really wish that Quake Champions ran in offline mode, then I might play it...as I find myself still doing the UT4 from time to time since it WILL run in offline mode, amazingly. BUT...I ran across this remake of Q3DM6, and it was interesting to me that the map still looks so much better on a 64bit Quake 3 exe!
I think on an engine and generation so drastically different you have to take a different artistic direction to the original, or at least build into the assets that come with whatever game it is rather than converting old ones.
I recall there being some pretty sweet conversions of DM6 for UT2004 as well. Interesting that the layout (or slight variations of) work so well across so many different games.