I actually disagree with this statement. The more detailed and precise an adventure is, the harder it is to make it your own.
I can see why you'd think that, but in my experience I don't have that problem.
Take, for example, the current crop of WoTC adventures for 5E.
I wish you wouldn't, if only because you are now debating based on evidence that I'm not familiar with. I've read little of the 5e modules, and so I'm out of my depth discussing them. But, of the three that I paid the most attention to, the rebooted Ravenloft, the Underdark sited based adventure, and the Chult/Acererak themed horror adventure, all three seemed to be things that you could easily mine for content or adapt to your game. None of them seemed like the sort of game that compelled you to run it in a certain way. I'd suggest as evidence, if you asked 20 different groups that had played the module to describe the events of their campaign, you'd get 20 different sequences of events.
Something I change in the first chapter, can possibly have a dramatic effect on the later chapters. Add to this, that I have to read the entire (massive) book to understand the adventure, before I make the adjustments I want to make... These require much more prep.
I would argue that you have to read any adventure a couple of times to even run it as intended, much less to alter it. The argument you make here though is strange, in that you are siding with B2 on the basis of its lack of content. That is to say, because B2 isn't particularly massive, and doesn't really plan to occupy the participants in the game for as long as the big 5e hard backs or carry them through as many levels and as many adventures, that it's better because it takes less prep. I can fully agree with you that B2 requires less prep to run than a full campaign book, even if you turned B2 into some sort of mini-campaign. But I don't see how that defends the text. It may defend the style of adventures that are smaller and less interconnected and so are better for more episodic play, and I might be entirely on board with that preference after having spent 8 years running an adventure path of my own design, only to frequently mourn that the structure of an adventure path tends to limit a player's choices simply because an adventure path provides a massive motivation to players to continue pursuing it as a primary goal - for most of those years the player's were convinced that the bad guys were making a 'destroy the world' doomsday device. The more episodic smaller adventures allow greater freedom to pursue player goals and make leisure uses of downtime, something I've come to miss (not because it's better, but just because it would be different than the fare I've been running).
It is easier to modify and adjust an adventure that has less moving parts and less detail.
I'm not sure I agree, simply because I've pulled modules out that have plenty of moving parts and adapted and 'sandboxed' them (at least in a narrow-broad-narrow framework).
Also, the DM input required of Keep on the Borderlands is the 'good kind'. It provides the stats and stocks the dungeons. It gives you details that are mechanically important and tedious to come up with on your own. What it leaves open to interpretation is what you should be doing on your own (and in a "basic game" is part of the lessons in teaching new DM's).
This is in my opinion the most interesting thing that you say, as it I think provides a unity between what everyone is saying about the module in this thread. I think the heart of what everyone is saying could in some way be found in this statement, and to the extent that I think it's just my opinion whether it is a bad module, or just someone's else's opinion as to whether it is a good module, the answer to why can be found in this statement. The heart of your statement is to say that, for you, there are certain sorts of content you find hard to create. You'll note that in this thread, and even more explicitly in other threads regarding B2, the heart of my argument has always been that B2 provides content which is easy to create. Both of us are saying that the module is valuable, or not valuable, based on our perception of what sort of content is valuable. I've frequently said that B2 is a 'atavistic' module that harkens back to more primitive dungeon designs that was thrown together quickly by Gygax to meet a deadline with little in the way of creativity on display, and that I'd expect any decent 15 year old DM to do about as well. It's far from the complexity and depth that you see from modules created in a parallel time frame by Jaquay or the Hickmans, or even really compared to some of Gygax's older work. It does for low HD demi-humans what the G series does for giants, only throwing the whole bunch of minitribes together willy-nilly in a small location.
But this assessment is based on an assumption of what is easy to create and therefore less useful, which I fully concede could vary from person to person. So if you are willing to go into more detail, I'd love to know exactly what you mean by details that are tedious to come up with, and what parts of the text that you both retained and found central to your play, and what things you find very easy to create.
The act of figuring out what is going on in these caves is, at least in my opinion, the primary lesson to be learned from the module.
I personally feel this argument would be bolstered if the text itself emphasized that. But truth is, the text of X1 spends more time talking about how import the act of figuring out what is going on on the island, at least as it pertains to how to hook the PC's into going, what they are expected to do their, and how they might set their own goals upon reaching the island. And I'd also argue that X1 has been more successful in spawning versions of itself, probably most deeply in the 'Savage Tide' adventure path, but reoccurringly over the years as it has been revisited in publication.
