That dice are rolled (in absence of the illusory railroad) shows that the referees vision is not determinate.
To me, there appears to be some tension here: if "GM decides" is the ultimate resolution rule for 5e D&D, then that seems to suggest that the GM's vision is determinate.The common view of d&d players is that ‘dm decides’ enhances the game if the DM can appropriately do that at the right moments for their table.
Even within the D&D-verse of RPGs, there is no single thing that is a "good DM/GM".There will always be bad DMs. I just can't imagine any game system, any set of rules, making a bad DM into a good GM.
Here is Lewis Pulsipher's description of a good GM for classic dungeon-crawling/wargame-style D&D, written in the late 70s (I'm referencing Best of White Dwarf Articles vol 1):
The referee must think of himself as a friendly computer with discretion.
That's not a bad job description for that sort of GMing. But it wasn't the only vision of GMing D&D around at the time - in the same article where Pulsipher wrote that, he criticised "the escapists" who "can be divided into those who prefer to be told a story by the referee, in effect, with themselves as protagonist, and those who like a silly, totally unbelievable game." Pulsipher writes that "I personally conisder the silly/escapist style to be both boring and inferior for any campaign, though all right occasionally for a weird evening."
And since the late 70s further GMing methods have been developed, most notably the sort of "indie" approach that informed my own (and plenty of others') GMing of 4e D&D.
I am not a good GM for wargame-style D&D, because I struggle to act as a friendly computer with discretion. I think I am not a bad GM in a style in which the GM is not expected to be neutral, but rather is expected to actively care about the characters as characters, and to show that care in part by lovingly confronting them with character-specific adversity. This is why I don't play B/X D&D (which needs neutral refereeing) but do GM Torchbearer 2e, which takes some inspiration from B/X but calls for a GMing style much closer to Burning Wheel (from which the game also takes inspiration).
I am 100% confident that system can help GMing. I've just given examples: B/X D&D is a good system for those who want to GM a neutral, wargame-style D&D experience; but is a pretty terrible system for someone who wants to GM a game of the sort that I used 4e D&D to run, or that I use Torchbearer 2e to run.
And during the period 2008 to 2012 (or thereabouts) many D&D GMs discovered that 4e D&D was not a good system for the sort of GMing they wished to undertake. In many cases they spoke about it quite vocally!