And Vault of Glass isn't a straight path?
The difficulty is completely subjective so it's hard to make such an easy judge on that. I would say Golgoroth is the most difficult encounter and most of King's Fall you can't afford any deaths otherwise you wipe. I would say that makes it "harder" than Vault of Glass. I don't see what parts would be "harder" aside from maybe more mobs in Vault of Glass to contend with?.
You're comparing "on farm" VoG to "early days" KF. Gorgons is the least straight-path encounter from any raid. KF has more exploratory space but nothing nearly as interesting as Gorgons. It took hours to understand initially but takes 30 seconds to clear later, which is perfect for content designed to be repeated weekly. Hive ships and pistons are great initially but tedious to repeat. KF struggles a lot with replayability, especially Oryx.
I agree difficulty is too subjective, especially since not many people remember early days VoG. Saying one death causes a wipe in KF but not VoG is not true. One death in early NM and HM VoG raids almost always caused a wipe since adds would pile up, oracles would get behind, etc. The team that 4-manned KF was easily able to stagger Doxology with only 2 people alive. KF only felt this way initially due to under leveled teams and inefficient strats.
Every VoG encounter has a brilliant snowball effect when people started to die: more pressure on remaining members --> more likely to die --> more pressure --> more death --> wipe. This effect happens naturally via encounter design, it's not hard-wired like one missed jump forcing a wipe on Daughters + Oryx even if everyone's still alive. People could still clutch out these busted VoG runs whereas KF is more binary for wipe vs clear. That's ultimately the greatest strength of VoG over KF, more freedom