Civ6 is better than Civ5 in every conceivable way. What brings people back to Civ5? Going back to Civ4 I can kind of understand.
You're entitled to your opinion of course, but "every conceivable way", really? How about:
* A World Congress where you can influence what is being voted on, as well as know exactly what you yourself are voting for?
* Less late game micromanagement?
* Cooperative projects?
* Having a bonus tree (Social Policies)?
* Systems being far more integrated, so that for instance, your actions in the World Congress affect diplomacy? Or cultural influence affecting support for your ideology?
* Better mod support?
* Having the Vox Populi complete overhaul, which improves and expands just about every aspect of the game while adding a host of new features?
I also personally find the art style much more pleasing, both the lovely art deco UI and the more realistic map style. The leader screens and wonder paintings are gorgeous too. And I prefer how religion works in Civ 5 over 6, as I find it much more natural and less micro heavy not to run apostles around shooting lightning bolts at other religious units.
In general, I think that Civ 6 is burdened with far too much tedious micromanagement, such as moving governors around, swapping out techs or civics so as not to waste research gained from eurekas and inspirations, and swapping policy cards in and out. The game has loads of features, but they never seem to be overhauled or refined after their first release, beyond a +1 here and a -2 there, and they are generally not integrated with each other. I guess new stuff is what sells expansions and DLC, as there has never been more content for a Civ game, but it largely just seems thrown in there, and the result is not necessarily a better game.
Note that I still would not say Civ 5 is better than 6 in "every conceivable way". I understand that people value different things, and have different tolerance levels for for example micromanagement. I personally think Civ 6 shines when it comes to how the civs themselves are designed, I enjoy district placement in the early game, I find the loyalty system to be good and something I miss when I play Civ 5, and the soundtrack is great. But overall, I like Civ 5 more, and Civ 5 with Vox Populi much more. Civ 6 for me is a game which had great potential from the start, but it wasn't improved by its expansions in the same way Civ 5 was.