Without city-states you are producing less food, less Faith per turn, less culture per turn, less happiness, less defenses etc. City states allow massive early growth. From my experience, you don't really need to get Colosseums and circus maximus, or circuses, or social policies for happiness. Do you realize how difficult it would be to keep growing to large heights and accumulating all areas while keeping happiness up without city states. City states in my experience are the absolute best thing to spend money on regardless of difficulty. Again, research agreements are nice, but how many times are you able to get a DOF with at least 4 people that are playing it peaceful and friendly without having to build up on a military. PT is not a needed wonder. If you really want a PT then build it, but you'd be better off focusing in other areas. WF will allow you to finish that entire Rationalism tree by coming in first with hammers which amounts to around the amount of hammers required for PT, maybe 100 more, but you can burn off writers and manage to get 3 or 4 social policies in 20 turns... I don't understand why this wouldn't be the focus.