The Wizard Talk and Astronomy
I can think of much worse scenarios than the ones that are currently being tested e.g.:
The Wizard is an unpromoted warrior on a city is a 1 tile island (so we can't use siege to bombard down the 200% defences due to a wall +castle+dun+citadel, and we have a worse amphibious penalty)................................. and also defending this city there is a stack of 3 rifles with all possible promotions.
If the City is an island that must be assaulted amphibiously, then Astronomy + Engineering + Gunpowder (all are techs that we are likely to get even if we perform an Astro beeline) + one more tech (Chemistry) = a solution to the City Defences: Frigates for Bombarding. Actually, if we are shuttling a lot of units there, then we only need 1 Frigate but a lot of Galleys or Galleons. Once again, Astronomy is better than no Astronomy, since it's an island in this scenario, right?
I agree that it is possible that there is more than one unit there and your theory of a Warrior Wizard is an interesting one. However, one possible flaw is that Barbs will upgrade a Warrior. So, if neilmeister really thought it through and played it out, he is not likely to have put a Warrior there, since that unit would not remain a Warrior.
While Cuirassiers are not exactly "pre-Astronomy" units, I think that it is fair to believe that we can safely tech to them before the end of the game, right? I mean, Nationalism for the Taj... a possible Liberalism on Nationalism or Military Tradition... taking Gunpowder in trade or as part of a peace deal... all are feasible and self-teching these techs would also be feasible.
Now, if we're going to build War Elephants, chances are that they will be promoted up the Combat line, right? All that we need are some War Elephants with 10 XP. As long as we don't use up that third promo then BAM, we have Amphibious War Elephants. Unfortunately, Amphibious War Elephants don't ignore First Strikes.
However, Cuirrasiers ignore First Strikes. War Elephants upgrade to Cuirassiers. Boom ba-da-BAM! Any War Elephants with Combat II and an unused promotion become instant uber attackers that can ingore the City Defences (via building just 1 Frigate), can ignore the Amphibious penalty, and can ignore First Strikes, all the while having base 12 strength with Combat II. We won't need very many of those, even if there is a stack of 3 Riflmen plus a Grenadier (the Grenadier being the upgraded Barb Warrior).
Again, we can win without very advanced tech (Chemistry and Military Tradition are not all that advanced for the end of the game, if you ask me).
I think that an even worse-case scenario is that the Wizard is in the middle of the continent and is SURROUNDED by Peaks.
Now, one possibility would be to settle a nearby City, Culture Bomb it, and thereby have the Barb units inside DIE when the City flips to us. Hahaha, pwned you.
If the Barb City is "not Atlantis" due to it staying at Size 1, then this possibility may apply, since a City that is surrounded by Peaks (maybe with some empty spaces next to the City for Paratroopers to land) is not likely to grow past Size 1, since there will be few or no squares for citizens to work.
Of course, neilmeister might have wanted to prevent THAT idea, so he might have made the Peaks too thick for Cultural Borders to reach the Barb City... requiring us to use either Paratroopers or Cruise Missiles.
Now, the question becomes: if we need Cruise Missiles and if we beeline them, will we really be better off by leaving the AIs alone until that time? Or will be we better off spending a good portion of that time razing AI Cities?
If the Barb City really is an isolated island, then we might need Astronomy to reach it.
Also, Physics is only a little bit further... Astronomy + Printing Press + Scientific Method lead to Physics, which would open up Airships... those would take the sting out of EACH defender, no matter how many Riflemen were stacked there.
So, in the end, we'll probably want Astro anyway. Why not leverage an early Astro to go razing at least SOME of these multiple AI Coastal Cities?
EDIT: Maybe there is only one Wizard unit but if he is in a Barb City, the Barbs might build more units between now and then. So, the earlier in the game that we strike, the greater the chances are that those Barb-built units will only be Archers or Longbowmen, instead of Riflemen.
EDIT 2: Also, we are Charismatic, right? So, Barracks + Stable + Vassalage + Theocracy = 3 + 2 + 2 + 2 = 9 XP = enough promos for Amphibious War Elephants/Cuirassiers (if there is a Horse Resource on the map) right out of the gate.