1. Civilization VI is a strategy game. It is not a historical simulation!
Oh sure. Let's just throw out historical civilizations, leaders, and the tech tree then. After all, it has nothing to do with history.
What? That's not what you meant? Well, why can't other historic things happen then?
If they are not impactful why bother them anyway?
One word: Flavor.
3. Crusader Kings II is not Civilization VI. There is plenty of RNG in Hearthstone for example.
Nor was I implying it was. But it
is another strategical history based game. And even though it has major differences with Civilization, it shows that you can reliably execute strategies even if there are severe random events. Much more influential than what I would suggest for Civilization VI.
And yes, Hearthstone has a lot of randomness. That's why it sucks so hard as a PvP game like most people play it.
4. Civilization is a snowball effect game. It means every random effect will affect your process from x food x hammer, in turn one to your win in turn x with x*n hammers and foods (sorry for huge simplifying). That means random effect will add x turns to your win. Try to win a game in Immortal where the game itself makes victory harder because it helps AI snowball effect with the additional settler, workers etc. Do you want another similar effect in a game?
And that's why events aren't "you lose a city" or "you get an additional unit in turn 5" (it would be very different if it would happen in turn 150, of course). Events need to scale with the game, and making them relatively small allows you as developer to let them occur often, which in turn means that the law of big numbers will even out the advantage or disadvantage you get.
5. There is no fun in losing strategy game because of RNG, and it would be very easy to create such RNG outcome in Civilization. Too easy to risk.
At the point where a random event loses you the game, the developer has made the random event too influential. Once again,
small events, no "get a free spaceship part" or whatever.
And let me come with some developer theory on my own (paraphrased from League of Legends developers):
There are two kinds of randomness. Good and bad randomness. Bad randomness occurs and you just have to deal with it. An example in League of Legends was innate dodge chance. Perhaps an example of something like that in Civilization VI would be a unit dying because he found no food in the desert (compare with what I proposed earlier; losing 25 HP). It happens, and you just get screwed.
Good randomness, on the other hand, allows you as player to react. For example, if you lose 25 HP due to no food, you can decide to carry on or perhaps heal up; it's still a strictly negative event, but there's something you can do about it. Beyond that, you could even present the player with several options, depending on the event. To take an example from the Civ IV: Colonization mod Religion and Revolution, shortly after founding a colony you could get an event where leftover building materials were found. You then get the option to 1. Build a chapel 2. Build a tavern or 3. Sell the materials for gold.
And
that is the kind of randomness you need. Either you give the player different options, or you give them setbacks that can reliably be overcome. You don't make them lose cities, you don't randomly kill off units, you don't burn down districts. No, you damage the unit, you grant a minor production boost, you give an extra population to a city. A good example of good randomness already in the game, in fact, is tribal villages: You know you'll get something out of it, but until you pop it you don't know what. Another example is barbarian camps: When a camp spawns, you know that you need to clear it fast or it'll start spawning units. So you have a potential major setback, but if you play around it, it's only a minor setback (because of diverting attention).
TL;DR: Randomness shouldn't be game deciding, it should add flavor to this
history-based strategy game.