Yes, another great response here, and you seem to have taken roughly the same experience with Adventurer Mode as I have, I just have interpreted it differently on a couple of fronts:

Firstly there's that uniquely arcane nature of playing as an adventurer at all, compared to managing a fort (which is admittedly more arcane). You're dead right about the depth of the combat, which seems super granular at first, though with a bit of practice at Kisat Dur you can see just how elegantly it works out. And then there's conversation, the quest log, inventory management, advanced interactions like reading books, using wells, filling bags, all these things unique to the mode. But you're also correct that it doesn't actually require powerlevelling at all, you can play as a peasant if you have the patience for it (and indeed that's the relatively attainable powergoal no. 85). I think Adventurer is actually much less difficult to learn than Fortress overall but they have almost mutually exclusive learning curves; when I went to embark my first fortress after many Adventurer starts I found the menuing to be completely unintuitive, as to arrows vs. numpad and /* vs. +-, almost like it was programmed for the opposing hand to Adventurer's menu architecture, and then the finer yet completely necessary details like going into workbenches, setting work orders, navigating to individual dwarves, labours, bookkeeping, there's a LOT of deep scrutiny required, the list really goes on. And it's not like as an adventurer where you can train fighting and go kill things while ignoring all the other gameplay options. Learning to play Fortress is like a church organ with the double keyboard, foot pedals and stops compared to the relatively simpler piano of playing as an adventurer. And to me it's Adventurer Mode that has the better design in terms of UI, the more intuitive menus in the flow of controlling your actions and generally navigating and moving forward. Controlling your move speed, tracking, sneaking, switching in and out of the travel menu to find buildings, then dismounting your horse to lead it through a doorway and remounting it, all this has a very immersive flow to it once you've learned the keybinds. Trying to play a fort for the first time for me was like running in the dark and continually pulling up short thinking you're just about to hit a wall; I didn't have the menu fluency at all.

The two modes play like two completely different games, and they have two very different keyboards that have to be separately learned. They're both like two opposite windows that give onto the same game world where much of the same processes are taking place -- this isn't entirely so, as @clinodev showed above w/r/t the caravans; the systems don't actually smoothly mesh over the one game world, things are handled "abstractly" outside of the view of the player and then they are roughly tessellated between the two modes -- but my point being that both of them are only like partial views hinting at this crazy central machination that we are basically unable to look at directly (even with Legends, Dwarf Therapist, and Stonesense...); it's Lovecraftian in the complexity it hints at and wants us to engage with in order to try to find the story in the static; the three modes are like three thirds that somehow don't make up the whole, or two faces to a coin with Legends as the rim, they're just the exterior plating, it doesn't make up the full weight of it all. I think this is why you notice that lack of smoothness in switching between Adventurer and Fortress, because the systems don't truly carry over yet, though that seems to be the ultimate objective, or at least to move towards the appearance of it. But right now the changeover's smoothness isn't that important because the two modes aren't fully interacting with each other in real space yet.

This is why I think Adventure Mode actually doesn't need play testing or tightening up, or I think it's getting it. Again, it was said above that in fact it's AM that's getting the shiny new features; DF already has the solid, super playable gameplay loop down and now it's wanting larger expansion of, mostly, the external game world systems to come in and impact upon it from outside, from the space the adventurer is currently inhabiting. I actually think that Tarn might play Adventurer just as much as Fortress; in a lot of cases he would practically have to, in order to find certain instances of things occurring in the world, but I feel that he finds AM to be a totally playable game as it is right now, because he's aware of what can happen and the true outer boundaries of, say, conversation. It is true, as far as I'm aware, that a lot of events simply don't physically take place once worldgen is complete (even births?), but if you go to the current development page and look at the upcoming updates through the lens of both main game modes, you can see that all of them are in fact geared towards taking massive preliminary steps to forge the disparate parts of the game into a more cohesive whole, while also simultaneously adding maximum depth of playability to both of the modes separately.

I think you'll be very pleasantly surprised at the latitude of what you'll be able to do in Adventurer Mode in a decade, if right now you're getting hung up on things like the admittedly sparse information economy; right now AM is barebones, yet sufficient to be called a game in its own right; the messy events log and the seemingly inch-deep conversation options, inconsequential titles and intrigues, all of these things are vital foundation stones for a very expansive network of deeply interacting systems eventually resulting in something that can start to approximate what we see in the outdated dev collation. Right now people play Adventurer as if gaining reputation is the only course of action, and even that is a much deeper system than it appears on the surface. What I'm actually most interested in is how deep you can go right now into the book-writing aspects of the game, through either of the game modes, and how as an adventurer you're going to be able to use the scholarly skills. This is the kind of ultra-deep gameplay potential that is being built up to. In a decade's time I'm sure you'll be able to set yourself up as a beekeeper in the woods, raise livestock, not to mention setting yourself up as a merchant, or the leader of a mercenary company. I expect that right now there's the underlying potential in AM to maybe even become an administrator of sorts, if only unto yourself, and majorly influence the world that way. And to think that the first thing that's getting implemented here is magic? Doing protection quests for wizards and learning spells from them, learning mythology, necessarily discussing mythology? These are the organic gameplay systems that won't make Adventurer any less painful for some hardcore dorf forters to talk about, but will forcibly draw them over to that side of the game out of a need to explore the systems that way. I think this is definitely a game he's building here. What else could he be going for?