Even for this setting I would,'t find that map style immersive.
You only have to look at vehicles in Fallout and they're on fire
+ Covenant, Bunker Hill, Vault 81, Quincy [destroyed by the Gunners very recently] and University Point [destroyed by The Institute in recent history] ... not to mention the mini towns / farms like The Slog, as well as the Settlements you can build that have great 'city' potential - Sanctuary, Sunshine Tidings, Starlight Drive-In etc.
There are plenty of towns!
I'm a hardcoe Bethesda fan but I agree there shoud be another big town like Diamond City on the map with a whole bunch of quests, if there was there would be no complaints
OP-
I agree that the size and scale of the cities has gone backwards in recent years. Oblivion had a horribly empty main city but the other smaller towns were very well done. Skyrim was a real step down from that- I still cannot believe that Solitude looks as small as it is. The High King living there for countless generations, surely not! Any man with an ego would never have stood for that. And the other cities of Skyrim. They were only big enough for one man and a mud crab.
Fallout 3 and 4 also have horribly small towns. Well, they should be villages, they are that bad. I get the whole down-town Boston thing and really enjoy exploring and hunting between the buildings. It is actually really fun. It is more the outside of the map needs to be expanded.
But, to compare these problems with the lack of vehicles. No thanks.
I love Far Cry 3 and I love Fallout 4. Let's just keep them the way they are.
Personally, I don't think it's too unlikely that there would be large numbers of raiders 200 years after the war. Throughout human existence, there have been nomadic or violent groups that have survived longer. Also, it's unlikely that the raiders' numbers would be soley comprised of people born into the group and, likewise, not all that were would remain in the group.
As for vehicles, I would agree that to manufacture them on any sort of scale would be nigh-on impossible, and to repair them would require expertise that would be hard to come by. That being said, it is a game. If I can pick up a 200 year old firearm and use it with no issue, I wouldn't be too upset with finding a nice set of wheels in the wastes.