doubt it's really game-changing. Rail is more expensive and the three other countries in the middle can be strong-armed and harassed into stalling or cutting this off.
Depends, cutting off strait of hormuz could easily change that calculus a bit. Things can get unpredictable from here on now.
from what i read, the Strait of Hormuz is mostly used for shipping to Asia now, with the US being a net exporter of oil, KSA and others getting more options to ship via the Red Sea instead, and overall blocking this would be a minor annoyance, not lasting long with 2 carrier strike groups on the way, and most to-be-blocked shipments going to China - shooting themselves in the foot. It seems the historical memories of the 70's mideast oil beef are just that. But what do i know.
Futures do not disagree with you atm.
Afghanistan? Probably not. The other two are bordering China. I highly doubt they'll bow to the US instead.
I don't think it's going through Afghanistan. It's probably just re-using Soviet railroads. But it is going through Turkmenistan, which is one of the craziest insane and most bizarre and unpredictable places one can think of, and Uzbekistan, which used to happily host US troops in Khanabad. Just a matter of some cash and some threats of sanctions with either one of those two.