What I would say is that this view is questionable. If the US does abandon certain regions, namely Europe, SCS, Straits of Hormuz, Korean Peninsula then how do we know that the dominant powers in those regions will behave fairly according to global law and principles? Russia, China and Iran have not proved themselves to be fair trustworthy influences. On the other hand I see the US as much further down the road in this regard having made mistakes in the past.
One view says that the US are in those regions because they are needed. If the US had no presence in the SCS for example would China have done what they have with the bullying and island militarisation? In my opinion yes. These powers are rising fiercely with imperialistic ambitions not fitting for this age but more appropriate to the early 20th Century. This calls for a strong super power like the US to equate the balance.
Now back to the topic of the thread. I'm beginning to see more and more some wider conspiracy here against the US and this probably more than anything explains why they have not been as assertive in Syria as many would like. What I'm getting at is that at virtually any time the US could be called upon to defend in at least 4 other theatres:
1) Middle East Straits of Hormuz
2) The Korean Peninsula
3) Ukraine or the Baltic Countries.
4) South China Sea.
You can bet that as soon as the US commits to one of these regions with a large military force the others will kick off. I would not rule out some wider sinister plot here. It would be interesting to know what others here feel about this. The US has allies in those regions yes and would not be fighting alone. Nonetheless they altogether would present an unpredictable drain on the US military machine.
Who's interest does the US serve in:
1) Middle East Straits of Hormuz
2) The Korean Peninsula
3) Ukraine or the Baltic Countries.
4) South China Sea.
It's own? Or the common good? If it doesn't serve US interests to be in those areas it wouldn't be bothered. It is not alone in that. Most, if not all, the nations are like that. The US, UK, Russia, China, France, Germany, Australia, Norway, Netherlands, Japan, NZ, etc., are only truly energised about a region / issue when it is politically expedient for them to, or they perceive it as affecting their national interest.
To be brutally honest, what really needs to happen in the Middle East now is for all the non regional players to exit stage left and let the locals sort it out amongst themselves with an arms and any form of aid embargo on the whole region including Israel. No arms, no money, no humanitarian aid, no political or diplomatic support, no emigrants / refugees from the area; nothing. It will be a real bloodshed, but it will be sorted, eventually. Then they can start again with a level playing field and a better attitude. The US will just have to bite the bullet, build a bridge and get over Iran. If the Iranians decide to nuke the US then the US retaliates likewise - quid pro quo. The US doesn't need anything that the Middle East has to offer now. It doesn't need its energy because it can supply its own or get it elsewhere. There needs to be a sea change of thought and attitude about this from the West, Russia and China.