This is where I am seeing a huge disconnect in the thread.
Yes, the entire idea is that sometimes you will be limited and that implies adaptation.
Virtually everyone agrees here.
But this means we have to ensure there are valid (read: not extremely unfun) ways around it.
For example:
Suppose there's only one strategic resource in the game, Firaxite. Every single unit except warriors and slingers requires Firaxite to be built. Some continents have it and some don't.
Is this a good idea? No, certainly not; the random chance of not having it would be an automatic loss. That's not very fun.
Now, let's go back to GS: the industrial and modern+ eras both have their version of firaxite: niter and oil. If you don't have niter in the industrial, your recourse is Pike&Shot and Field Cannons. Not great but you still have battering rams.
If you don't have oil in the modern era, your recourse is AT crews and... field cannons. (You don't get MGs until atomic.) How's that going to work against infantry and tanks?
You also lack artillery so you cannot actually capture urban defenses cities to get the oil you want. In a balanced game with humans or the sought after competent AI, you would find, as
@kaspergm said, that the joke is on you.
The discussion about resource distribution and the one about combat resource balance are very much tied. But even ignoring that, if you lack iron, you might still get horses. But sometimes you get neither. How likely should that be? Sometimes the map generator drops you on a desolate tundra island too, but that's pretty rare. Should it be 1% of games? 30%?
If it's even 5% of games, then 1 in 400 players (many thousands of people) will have had their first
two games of GS without any strategic resources near them early on. They will be frustrated. What about players who play Prince in such a way that the AI keeps near them in tech? They will feel hosed in any war. I myself have never had this problem yet, fortunately.
The trade side is also not as good as it could be, especially for fuel resources. They're all over the place on prices and even availability. We all know the AI is pretty weak on trading generally. There's no "world market" where you can guarantee some access for a price. There's no access guarantee and there's no cost guarantee. You can end up in a situation with no options. Unlike starting on tundra purgatory island, you've invested 5 eras into the game already. This creates a lot of negative fun. It's not about whether this should be impossible - but how (un)likely?
We may not even need to change the map system - even just moving discovery of oil back in the industrial so you have real time to react, for example, could be enough. (I don't actually see much issue with iron or horses. It's the resources that are the only one in their entire era of units, because you get no fallback but AC+ranged line.)