Do the AI civs now start with even more units in R&F than they did before in relation to the city-states? Or are the AI civs simply more aggressive regarding city-states in higher difficulties than King?
Also, is this situation impossible to strategize for? Is there no way for a determined human player to protect one or two city-states that they can concentrate on? Is there no chance of liberating them? Are they all being conquered long before the human player can do anything?
If I step back from the details, all I see is that on higher difficulties the game has a method of reducing bonuses the human player can be quite good at exploiting. If this is new in R&F, I suspect it is in response to some level of fan comments.
For those players who regularly start conquering CS's right off the bat and have complained about the AI's lack of aggression, I would expect they would be pleased. Unless, of course, they are now peeved at the AI for "picking the fruit" before they could.
It's quite possible to strategize for it, but the only meaningful interaction is now war, either to protect or to liberate. Since you cannot deter AI from attacking (they can't even easily consider suzerain military might before declaring, as suzerain might change any time), your only option will be to declare war before the AI take the CS (and take all warmongering penalties even if you don't take any cities), or liberate it afterward, in which case all envoys will have been reset.
So basically the whole envoy game disappears. Unless you are already all around a city state and can physically prevent its conquest (you'll have to close borders), it makes no sense to invest any envoys since you can loose them any time. I don't know what changed to make the AI so much more aggressive toward them (I'd say Deity AI usually took one city state close to them before R&F, on average).
If you combine it with the conditioning of the bonus on district buildings, envoys now have a very marginal purpose after the very early game (when you have no envoys anyway, outside of first meet and quests)
Of course you can still interact with city states, but the influence/envoy game system is useless, at least in Deity, outside maybe strange games where city states all spawn isolated from most AI. I have seen that happen before, but the new algorithm for start placement in R&F should prevent that now anyway.
The only uses of city states that were really strong were very specific and hard to achieve anyway (globalization rush), other than papal primacy which has been removed from the game anyway and still required the right religion.
Specific Leader abilities regarding city states (Pericles) are currently useless as well.