P.S. I just saw that you joined this site a mere 4 days after I did. I would say that is crazy but it is also Civ 4's release date.
Haha, well investigated - did you also take a 6 year hiatus?
Civilization departs so much from history, not just in what happens, but also in its fundamental mechanics, that talking about realism or historical accuracy makes no sense to me.
Being historically flavoured is the closest that Civilization comes to history. This flavour is vitally important to Civilization games, and is definitely changed by civ-swapping. But its impact is almost completely unrelated to questions of accuracy, because there is virtually none to speak of in the game anyway. Whether you like the new flavours or not is completely subjective, so there's nothing worth arguing about here.
The problem with bringing in a 30 year old phrase into this is that it's simply irrelevant to the conversation. It's an attempt to go from "this change is big" (which is true, though probably not as big as we are all making it out to be) and "I don't like it" (perfectly fair) to "therefore it's bad". But the existence of an old phrase does nothing to back up this inference. It just demonstrates that the change is, in fact, a change. True, as any truism can be, but that's all. It come's down to Voltaire: “A witty saying proves nothing.” Or, for a modern example, it's trying to convince a jury by saying "If it doesn't fit, you must acquit". Short, catchy sentences sound profound (and are fun to say!) but they're not good reasoning.
But even
if we were to take "Build a civilization/empire to stand the test of time" as an inviable holy guideline about what a Civilization game must be about (which I don't think we should), then I'd argue that Civilization 7 doesn't break that. Obviously not for the "empire" version, and not for the "civilization" version either. It's just that the historical-flavour of the civilization we build is no longer taken solely from the game creation screen, but gets built on during the age transitions. Lets not lose track that none of us have ever built Mongolia. Mongolia is a real thing outdoors. What we've built is
our own fictional civilization, within the confines of the game. We're still going to be doing that in Civ7. In fact, we're now building a civilization in more ways than before because we're building up not just its cities, units, technologies, etc.. but also its identity by adding in elements (both in terms of mechanics and of flavour) from other civilizations. Sure, by adding in flavour from other sources we're changing the civilization as we're building it, but that's building it none the less - giving a house a lick of paint and changing decorations doesn't stop it being the same house. There's still continuity in the thing your building, and the sum total of what you're building is still singular. Besides, in prior versions of the game, when you conquered the world as a Fascist Jewish Genghis Kahn who had built the Pyramids and was mass producing aircraft carriers from your island capital, it's clear to me that your in-game civilization had been influenced by more real-world civilizations than just Mongolia too.
Now it's possible to take "Build a civilization/empire to stand the test of time", reduce it to only "Build a civilization to stand the test of time",
and interpret it such that the "civilization" mentioned in it is precisely the civilization you pick in the game creation screen in its purest form; then Civ7 does break that phrase. But I don't believe that the old marketing phrase in its widest form should be placed an untouchable altar, and I certainly see no reason that one specific interpretation of one specific formulation of it should be either! Which is the exact sentiment I expressed in my prior post, just expressed in too much detail now lol.
If anything breaks that famous catchphrase it's not the civ-swapping. It's the crises. Because they force us to partially-fail the test of time twice. Although I'd argue the fact that you're being stress-tested means that you're actually being put through "the test of time" in a way that we rarely were in past game. From a historical flavour perspective (let alone a gameplay one) partially failing multiple times before succeeding sounds awesome
to me!