I agree that hexcrawl rules were not as detailed as rules assuming the party was in a dungeon. However, you are assuming a somewhat static dungeon where monsters wait behind doors for PCs to discover them, and many of the better adventures of that time neither advised or allowed that. DMs were encouraged to create movement in the dungeon, to restock it, have the enemies use tactics as if they were defending their homes, and so forth. Not to mention, the DM is assumed to literally create their own dungeon in 1e, so I’m not sure I agree with what you’re saying about the players control when encounters occur.
The more the GM treats the dungeon as a "living, breathing world", the more the expected game play will break down.
Here is Gygax's advice to players (PHB pp 107, 109):
First get in touch with all those who will be included in the adventure, or if all are not available, at least talk to the better players so that you will be able to set an objective for the adventure. Whether the purpose is so simple as to discover a flight of stairs to the next lowest unexplored level or so difficult as to find and destroy on altar to an alien god, some firm objective should be established and then adhered to as strongly as possible. Note, however, that inflexibility or foolish stubbornness is often fatal. More about that a bit later. . . .
A word about mapping is in order. A map is very important because it helps assure that the party will be able to return to the surface. Minor mistakes are not very important. It makes no difference if there is a 20' error somewhere as long as the chart allows the group to find its way out! As it is possible that one copy of the party's map might be destroyed by mishap or monster, the double map is a good plan whenever possible - although some players have sufficiently trained recall so as to be able to find their way back with but small difficulty, and these individuals are a great boon to the group. If pursuit prevents mapping, always go in a set escape pattern if possible - left-straight-right-straight, etc. Such patterns are easy to reverse. In mazes always follow one wall or the other, left or right, and you will never get lost. If transported or otherwise lost, begin mapping on a fresh sheet of paper, and check for familiar or similar places as you go along. Never become despondent; fight until the very end. . . .
Avoid unnecessary encounters. This advice usually means the difference between success and failure when it is followed intelligently. Your party has an objective, and wandering monsters are something which stand between them and it. The easiest way to overcome such difficulties is to avoid the interposing or trailing creature if at all possible. Wandering monsters typically weaken the party through use of equipment and spells against them, and they also weaken the group by inflicting damage. Very few are going to be helpful; fewer still will have anything of any value to the party. Run first and ask questions later. In the same vein, shun encounters with creatures found to be dwelling permanently in the dungeon (as far as you can tell, that is) unless such creatures are part of the set objective or the monster stands between the group and the goal it has set out to gain. Do not be sidetracked. A good referee will have many ways to distract an expedition, many things to draw attention, but ignore them if at all possible. The mappers must note all such things, and another expedition might be in order another day to investigate or destroy something or some monster, but always stay with what was planned if at all possible, and wait for another day to handle the other matters. This not to say that something hanging like a ripe fruit ready to be plucked must be bypassed, but be relatively certain that what appears to be the case actually is. Likewise, there are times when objectives must be abandoned.
If the party becomes lost, the objective must immediately be changed to discovery of a way out. If the group becomes low on vital equipment or spells, it should turn back. The same is true if wounds and dead members have seriously weakened the group's strength. The old statement about running away to fight another day holds true in the game. It is a wise rule to follow.
On the other hand, if the party gains its set goal and is still quite strong, some other objectives can be established, and pursuit of them can then be followed. It is of utmost importance, however, to always carry slain members of the expedition with the party if at all possible, so even if but a lone character is lost, it is usually best to turn back and head for the surface.
This advice, which is all about how skilled players should take control of the triggering of encounters as much as possible, by building up and deploying knowledge of the dungeon and its inhabitants while managing their exposure to wandering monsters, becomes worthless if the GM changes things to such an extent that the players' knowledge is not reliable and able to be deployed.
Some of this is a matter of degree. For instance, an ignominious retreat from the dungeon might reasonably trigger some changes to the dungeon, as a type of loss condition. Or it may be that part of the information a skilled group of players might pick up could include information about (say) a roster, or the movement of some forces from place A to place B.
But if the changes the GM makes are reflecting behind-the-scenes conceptions that the players don't and can't readily have access to as part of their play, then the basis for skilled dungeon play becomes undermined.
A party explored more in 1e because they didn’t want to miss gold. A party in subsequent editions didn’t need to explore as much because the story goal drove them forward - they just need to reach the boss lair or save the princess, etc, and once that’s done, the rest of the dungeon can be skipped.
What you are describing here is exactly what I am talking about: instead of the game setting the goal (ie acquire treasure and, thereby, XP), and the players making decisions about how to achieve that goal, the GM is setting the goal (fight the boss, save the princess) and the players are not choosing their goal nor how to achieve it.
The GM literally created the map and stocked the dungeon, and that basic idea has never changed, whether it’s a site based adventure or a story based adventure. What changed is the pacing and need for treasure.
In a dungeon crawl, as played in accordance with the rules of the game and Gygax's advice for skilled play, the
players will exert considerable control over the pacing, the scene-framing etc. They draw their maps, collect information, make decisions about how to explore the dungeon, when to withdraw to rest, etc.
In a "story based adventure", the GM controls all those things. There is no structured procedure of play that permits the players to exercise control.
That is a fundamental difference. The style that emerges as predominant in the 80s, and that becomes "official" with AD&D 2nd ed, puts the GM at the centre of all the events in and outcomes of play.