I won't go back to vanilla, but it isn't great
Civ 6 Vanilla has a lot of design flaws which leads to a unique optimal strategy : spam military units, crush everybody, then win as you want (why no drawbacks in conquering a large empire?). UI is terrible, you should be able to play your turn 3x faster. Some good additions like the district system. 1UPT was a great idea until you realize AI could not manage it at all.
R&F is adding stuff without any critical issue:
- loyalty is the best idea but should be linked to cultural/political power of a city and not only or not at all to his population size;
- same 7 governors for all civilizations doesn't make any sense, poor design by the way, need too much micromanagement
There is a lot of good, interesting, great potential stuff in Civ 6 Vanilla, R&F and coming GS, but all that stuff should be reworked at the light of the experience in a new game (Civ 7) with healthier core mechanics.