Pointing to the existence of these games does not address his point though, if anything it proves it. He's saying that C&C, as it exists precisely in the sort of cRPGs that you mentioned, is a rather inadequate attempt to emulate the player agency and freedom that is possible in PnP RPGs. C&C in the full sense happens, as @Covenant pointed out, when consequences are able to keep up with choices. When all you get from a choice is an ending slide, an alternate campaign endstate, or some unique dialogue lines from NPCs, the sense of agency evaporates because it is all symbolic, a token.
True C&C means that choices drastically alter the ongoing gameplay experience and the consequences are not thus the end of a given gameplay experience but rather its continuation. This kind of C&C absolutely is possible in PnP RPGs, as illustrated by the off-kilter campaign story that Covenant linked to. Something like that would be far more fun and engaging than simply unlocking a different set of quests after a key choice, quests that by necessity are handcrafted and predetermined: the agency here is illusory, and that due to the constraints of the computer gaming medium.
The reason for this is that PnP games run on the engine of human imagination, while computer games would require a prohibitive amount of resources poured into them to approach even a fraction of that kind of player agency. Even if cRPGs were to attempt to set up that kind of platform for player agency, doing it in the Black Isle/Iron Tower style would be wrongheaded. Handcrafted quests and dialogue trees are not the gateway to more player agency, if anything they perversely tend to introduce a very peculiar kind of railroading that, while distinct from that seen in linear games, is just as insidious and restrictive as the latter because the only advancement options are through the quest network and there is no option for the player to strike out on his own and forge his own stories through the mechanics.
It is by introducing robust gameplay mechanics that PnP C&C can even begin to be rivalled. That was what Covenant was talking about when he mentioned Sega Bass Fishing, Harvest Moon, and dating sims. To match the emergent gameplay of PnP you'd need a mechanical diversification that allows the players to play out unexpected stories that the game designer would never even see coming. An RPG with fishing mechanics and a character system that allows fisherman builds would allow you to play out that particular story instead of giving you an alternate ending that says "and he dedicated himself to fishing for the rest of his days". If a game had Rise of Venice style mechanics that allowed you to build a trading empire maybe you could even come close to replicating that salt trading empire from the PnP campaign mentioned above.
In this sense, games like Deus Ex have come closer to true C&C than the likes of AoD, because they introduce a mechanical diversification into their engines that allows the player to express their role through the different ways of approaching problems and navigating the levels. Of course, these games have their failings too, as they often don't encourage the player to specialize, but the LGS/Ion Storm school comes closer to the spirit of PnP than the BIS school does.
There are two further points to clarify here. First, no, RPGs are neither fishing games nor commerce sims - and they'd be worse at implementing such specific mechanics than dedicated games - but they are the kinds of games where you'd have the choice to play as a fisherman or a trader (at least when sufficiently expanded, it goes without saying that no RPG allows these two options, plus the convential suite of combat options, not that I know of anyway). Second, yes this kind of thing would be extremely ambitious, and perhaps impossible to pull, but if one wanted genuine player agency, it would be the way to go. In any case approaching said agency through scripted quest/dialogue-based design would not be much more plausible, if at all.
If that is the case then, and matching the freedom of PnP is impossible for cRPGs, then it seems that the more logical course of action would be to take inspiration from the early, Gygaxian PnP modules that focused on tactical combat, character building, dungeon crawling and exploration, as these translated very well to the computer gaming medium from the very beginning, as the Wizardry franchise illustrates.
What’s the goal of reactivity/C&C? Well, why have any story at all? It’s to make the player give a fuck. The more interactive the story is, the more engaging it is. “These guys are trying to kill me because that’s the plot” is less fun than “these guys are trying to kill me because I made a choice that pissed them off.”
It seems that you think a narrative and/or reactive focus in RPG design is primarily about engagement. Leaving aside for the moment the tension that often arises between reactive and narrative-driven design, I am not sure I would say a good story or reactivity make for a more engaging game.
If engagement is about involving the player, then why not instead make the game focus on the gameplay mechanics? After all, the main difference between reactive narratives and linear narratives is that the former require more input for the player, while the latter renders him passive.
However, if player passiveness is the bane of engagement, then there is no reason to extoll reactive dialogue challenges and branching quests as a superior alternative to combat, exploration, and character building (the core triad of RPG gameplay), since the latter tend to involve more input from the player both in terms of the sheer amount of interactions that the player can undertake and of the variety and emergent value of said interactions. I personally find it easier to be engaged by a game with strong mechanics and thoughtfully designed combat and exploration content, even if it has weak storytelling/reactivity, than by a game where the opposite is the case. Bad combat and exploration can quickly put a damper on the moment-to-moment experience of a game, something that decreases the engagement of large swathes of a campaign.
Sure, some might say, "a good game should have both good gameplay and story", which may be true, but is rarely the case in practice. There are a few exceptions such as Fallout, but for the most part story-focused games tend to have terrible gameplay: PS:T, Kotor 2, Vtmb, Witcher 3, the list goes on. In practice, devs have to choose something to focus on and pour their limited resources in it. Games are never going to be as good as books or movies when it comes to storytelling, so the focus shouldn't be there.
Yes, games offer certain possibilities (through interactivity) that are not present in those media, but they are far too limited to compensate for what is lost by not going either for a dedicated narrative focus (as in literature and film) or a full commitment to mechanics-driven gameplay. Not to mention that, as we have seen, even in the case of interactive storytelling, videogames get trounced by another medium: PnP.
None of this is to say that a bit of C&C or story elements are bad for a game, on the contrary, they add to the experience when they are introduced in a way that is both harmonious with a game's core design and do not drain an inordinate amount of resources from the development process, but in the context of videogames at least, they should be considered primarily as flavor, or gravy, if you will. They should not be the design focus of RPGs.That place belongs to the triad of combat, character building, and exploration.