Actually if you are invested in the main quest, there are plenty of loot bumps along the way that will make the rest of the game easier which explains why I never really encountered a single ammo shortage in my first playthrough.
Anyway, even if you don't want to advance the main quest, the longer you delay visiting DIamond City, the more you will feel the scarcity of resources since you cannot dump unwanted loot to convert them to bullets as easily. Not to mention the majority of EXP boosts comes from quest completions which Diamond City has plenty of.
There are some good things though. Building is fun until you hit your settlement limit, or have to deal with 10 different bases.
Is it possible to just migrate the settlers to a single place? I often don't see the point of splitting up the settlers in smaller numbers across larger number of settlements, only to be constantly reminded that I need to provide them with defenses and other time consuming upgrades.
Anyone bummed that all the human enemies are essentially either gunners or MAINLY Raiders? Wtf happened to stuff like Freeside Thugs and the like? After starting to feel the burnout things just keep adding up for me. And I go back and realize how much was removed.
If you follow the main plot line a bit more, there will be a few Raiders, Gunners (basically mercs), Mafia men (SMG toting fedora men), and a few more. What you described as variety in enemies in previous games seem to be 'dudes in different faction'. I wouldn't want to spoil it, but the factions don't actually vie for control for Commonwealth so openly like New Vegas' factions did, hence you saw no uniformed men (Legion vs NCR) fighting each other. And yes, I feel you. I also wanted a deeper 'faction' interaction, but you hardly get into it unless you advance into the main quest.