From a historical perspective, that is true for iron because it's so widespread that you can basically find it everywhere in burning ground at a very high temperature in an oven, but that wasn't true for copper and tin during the bronze age. It wasn't true for obsidian even before that. The History of Civilization has been widely driven by the need to have access to always more resources, and that since Upper Paleolithic. It has lead to the rise and fall of civilizations, be that with spices, coal or even oil today.
Now from a Civilization gaming perspective, honestly, I don't know because it seems that people are looking for completely different things behind such a broad concept. It really entirely depends on what you want to focus on.
From a historical perspective, before the Industrial Era anything you really wanted and were willing to pay for, somebody was willing to supply it. Don't have copper? The Phoenicians will haul all the copper you want from Cyprus and sell it to you - and you do not have to establish a trade route or build a boat or do anything except pay the price to get it. Don't have tin? Somebody will pack it in from Afghanistan or Cornwall as long as you are willing to pay for it.
Before the Industrial Era requirements, nobody needed iron, tin or copper in amounts greater than packloads - the amount of iron necessary to fully equip a Roman legionary with armor, weapons and equipment was less than 50 kg, even as raw ore, and that could be loaded onto any donkey - which had been domesticated by 3500 BCE largely for that reason: they made very efficient pack animals for long distance, overland trade (the camel was domesticated much, much later specifically for trans-desert trade routes). An entire Roman Legion could be equipped with less than 250 tons of iron ore, carried on 5000 donkeys or about 8 early cargo ships (30 tons/ship seems to have been fairly common, almost 'standard' since Minoan/Phoenician Bronze Age models).
The big change in trade goods came with Industrialization. A single ironclad required over 1000 tons of iron goods, A single kilometer of railroad track - without cars, locomotives, stations or any other infrastructure - required 100 tons of wrought iron or steel, and that's by mid-19th century - it at least doubles by the early 20th century, as rails almost double in weight and size.
Suddenly the amounts of raw materials needed to do anything meaningful increase by an order of magnitude, at least.
But here is the other point to Trade and raw materials: everything has a substitute. Can't get Tin for your Bronze? Arsenical ores can be used, or Zinc to make Brass as a substitute. Don't have enough petroleum? Coal can be processed into a substitute, and was in the 1940s in Germany. Niter was originally found in natural deposits, then manufactured in Nitraries, finally manufactured artificially using the Haber Process and other techniques for both fertilizer and munitions.
Civ VII's system is perfectly adequate for the first two Ages, when quantities required were small or moveable (like sheep, cattle and horses), but IMHO needs a revision for the Modern Age.
Modern Economic progress was and is dependent on getting massive quantities of certain materials, primarily Iron, Coal and Oil, but also including a multitude of other raw goods (The US Strategic Bombing Survey identified over 80 'necessary' materials needed by German industry in WWII), most prominently Rubber, Aluminum, and very specialized materials like Chromium, Molybdenum, Manganese, and Tungsten. The game does not need that level of detail, Thank Dog, but the contest for coal, iron and oil supplies was a major part of strategic thinking throughout the 19th and early 20th centuries, or the majority of the Modern Age in the game.
Also, having an entirely 'new' system of raw materials supply for the economic base of the Modern Age would give gamers an entirely new set of Age-related problems to solve in that Age. Do you search out major iron, coal or oil supplies on the map and seize them? Or do you set up to manufacture Substitutes by, say, building a great network of Technical Schools and a very advanced Chemical Engineering establishment (the 'German model') to feed your industry and economy?
I'd gladly play a game with hard ancient focus where things such as copper and tin are rare desirable resources, but obviously in civ pre-iron ages are too small part of the game to warrant that.
