These are all minor variations on the "DM can fix anything!' point.
I would argue that this was one of the goals of 5e.
One thing that 3e and 4e attempted to do was remove DM decision making from a lot of the game. It used an increasingly codified set of rules to create balanced and fair play.
However, with the rise of computer games and MMO...the pen and paper market had a realization. How does their product compete? I mean, I can have much faster combat, much more detailed character abilities, much more complicated math in a computer game. So what's left?
The answer is....a human DM. The best AI out there is still just plain I, a DM can adjust the game on a dime, can handle any scenario, can allow players to adjust their character beyond any codified parameter. The human DM is the reason that pen and paper games can still compete in today's market.
So I do believe that 5e has gone back to the early days of Dnd, where DMs are given the responsibility to handle corner case scenarios. That said...the system doesn't expect DMs to make calls on every little circumstance. The game still attempts to provide us clear, organized rules that can handle the majority of situations. But it does take the kid gloves off a bit...and says "if a situation comes up that isn't quite working...the DM has the authority to do what needs to be done for the good of the game".
Going back to the golem scenario. The MM provides us this monster, which is different than your normal beat em up orc or kobold. This monster is special, and can hurt players in a way a normal monster can't. The DM who would use such a monster has to decide how to handle it:
1) Don't use it. It doesn't fit the game, so its left out. Plenty of other monsters in the book to use.
2) The party fixes it through their own roles.
3) Its fixed through magic items.
4) Its fixed by hiring someone.
5) Its fixed by a special quest.
6) Its fixed by a long bout of rest under special care.
7) Its not fixed, and becomes a special plot point in the game.
All of these options can work, and its for the DM to decide which options work best for his game.