To me, and I would think that to the great majority of people who play RPGs, those are meaningful differences. Another team might trick the baron and Wachter into taking each other out. Or take the side of the Baron’s young son against the other factions. Or, just skip Vallaki altogether.
And that is just one aspect of the AP. Multiply that by any amount of encounters and you get a constellation of different choices, actions and outcomes based on what the party did.
The implication of this is that in any adventure with fixed encounters, the characters are interchangeable and their decisions are meaningless.
Obviously, I disagree. I think most RPG players would also disagree with this interpretation. It goes without saying that “meaningless” and “interchangeable” are subjective terms.
Well, I cannot speak to the referenced AP, I know nothing about it. However, this sort of thing is VERY tough for adventure writers to pull off, at best! For example, in the 4e era there was a Dungeon adventure, Dark Heart of Mithrendain. For some reason I got bored or lazy or something and decided to actually RUN A MODULE! This never happens, lol. I learned why, which is that it was as much work as making it all up myself. The adventure is actually pretty flexible in that it revolves around a bunch of intrigue. Mithrendain is a fortress city that guards the main entrance to the Feydark, where the Fomorians lurk, and there's a 'gate' which the city defenders protect. Some of these defenders have been corrupted, and there's a faction who knows this, but nobody knows who is trustworthy. So, you'd think this would be a very flexible sort of setup where the PCs are brought in by the 'good guys' and set to try to uncover the bad guys. The problem is, in the end you WILL end up in a final confrontation where the party has to venture into the base area of the Fomorians and kick butt. So, NO MATTER WHAT happens in the "James Bond Phase" of the adventure doesn't REALLY matter in the end. Yeah, maybe slightly different assassination attempts will happen and some of the intermediary fights and whatnot might or might not happen as laid out, or you would have different ones, in the end, like almost all adventures, there's a denouement, the big bads come on stage and get their moment.
I subverted this by adding a lot of very character-specific elements. The Eladrin Wizard's family is one of the clans, are they being subverted, are they dupes, can she trust them, and if so who are the enemy, and will they even survive this? The warlock was getting major bad vibes from 'the stars' wanting him to do their bidding, why are they interested in this? He decided to break free of their influence, and what do you know, a covey of hags showed up to offer him a way to defeat the Fomorians, all he had to do was accept this one little gift.... (he ended up with a secondary Fey Pact, which was pretty cool). The swordmage found out that her mentor opposed the city defenders, why? What were HIS motives? So, that part of the adventure got a lot more interesting than the rather shallow and meaningless stuff that was written into the adventure (it has some decent useful NPCs and factions, there's just not much to make the PCs care about them besides die rolls). EVEN SO the finale was still fairly much of a set piece. The option existed for the PCs to try a 'third way' where they would change the system that governed the city, but SOMEONE has to kick Fomorian arse, unless you just wanted them to win (which I couldn't really come up with a reason why even stupid crazy people would want that, Fomorians are nobody's friend).
Anyway, my point is, adventures are pretty strongly constrained to have a rather narrow fixed set of contemplated outcomes. Going 'off the rails' or heavily customizing is cool. I think they can provide some material, but honestly its hard to see very many successful adventures in any classical sense being written for most Story Now play. Something like
@pemerton's favorite Arthurian Romance game, Prince Valiant, is probably about as ideal as it gets, the sorts of action that happens in that milieu is pretty strongly stereotyped, and a lot of what matters is more HOW you did something and what its effects on the character were, vs lots of doubts about the basic plot and who will fight who, when, and where. Of course that also means there are only a very few classic 'patterns' for adventures to follow, unless you start pushing the boundaries of the genre pretty far (maybe by incorporating adjacent types of material from a wider region/time periods).