The real-life Romans disagree.
Maybe the sentiment towards the empire/civilization project but there are other aspects.
Romans were adept in keeping the people satisfied with colosseums, games, sanitation, bath houses etc. Internal affairs demanded the plebs to have more say etc. Living during Octavian and Nero would be quite a difference aswell. Empire mismanagment should make unhappiness IMO.
Also, romans had some serious problems when grain shipments were disrupted from Egypt for instance. There are secondary effects to war, such as the need for food and personell for armies, those priorities can make citizens very weary o the situation. If not Rome have had the Praetorians keeping order we probably have had seen alot more riots.
On topic:
First priority is luxury-aquisition. Settle, conquer to get resources under your control. Trade and city-state alliances are next.
Second priority would be to build at least colosseums in most cities.
After this we get issues, I would not object to a compromise formula between empire-wide happiness and the old system. Each city could have a balance but all

and

should be counted against eachother and produce the national happiness number. In this model you would require to have luxuries interacting differently with each individual city rather than have a set quote of maximum empire-wide happiness possible to produce from luxuries.
Also, is it +5 from each resource on every map-size?
If this is true, it's obviously not right and needs to be adapted to map-size.
Last of all. I think forbidden palace is slightly unbalanced, it seems to be almost required for large-scale warfare and we get only
one since it's a wonder. Wonder-rush and winner-takes-it-all...