Not sure how an unrest period would gel wth the loyalty mechanic and free cities.
Yes, true. Well then, loyalty mechanics could be revisited and deepened. Loyalty could be made more sensitive to long-lasting lack of amenities, and there should be, perhaps, a representation of nationality of the pops, living in a city, with certain impact on loyalty, as well as other factors.
As for this Tall vs Wide... I see it as a bad dream, some sort of obsession, an affliction that Civ V brought upon us, and now players would just not let go of it, as in some curious case of the Stockholm syndrome.
I do believe it should be better to have more of everything than less of everything. You could make less of everything work to 'win', as it is now in Civ VI, but having more of everything should be better. However, it should be rather tricky to keep that more of everything in one piece and work efficiently together, and that's what is currently lacking in Civ VI. There is no internal tensions, there is no fall.
Expansion should be rewarding and encouraged, but large empires, especially those built on several conquests, should be quite difficult to keep together. For me it would be much more interesting to get a large empire and try my best to hold it in one piece, not letting it fall apart, if I could.