I picked all the conversational options, other than Do Nothing; eventually I ran them all out and was left with Fight.
You are not aware of Conversation Battles. Have you ever done the Dog Days quest? Did you try to do it without fighting Hethia, and without getting Sanders to complete the quest for you? That, of course, is done by listening to Garret say that she's down by the banks between 16:00 and 20:00, heading there, and selecting the Parlay option. If you did, then you can engage in a basic convo battle. It's extremely simple and easy, considering that it's literally impossible to fail unless you repeatedly select wrong answers that you already selected another time, but it serves its purpose as a convo battle. You talk, you need to select the right answers, if you don't, you take resolve damage and need to go through that bit of dialogue again.
I've never done the centaur dungeon, but I assume, given how everyone else is responding, that this is also a convo battle. I believe that they have likely played this game for a long time, for several years and perhaps completed the COM (Definitely Emerald), like I have. Considering how you're talking about the conversation, you don't know about conversation battles, likely just not ever doing the parlay option of Dog Days. I'd get why this would be confusing or difficult for you, then, because I doubt it's as easy as the Dog Days Debate, so rather than an introduction you're getting plunged in head-first. I'm not sure what advice I can give you to fix this, aside from what the others are saying: Don't just blindly pick everything, pay attention to the conversation and motivations, and figure out the order you're suppose to pick choices. Several are likely incorrect options, so don't go back and repick them too.
And it's bad game design to treat "lose the game to gain knowledge, then restart and use that knowledge" as a deliberate tactic.
Dark Souls isn't a perfect game, but it's also one of the most well-known and well-liked examples of this design that I can think of. Not to go too in-depth, but basically, the boss fights are about learning how to counter the boss, both in learning its moveset and how to dodge
and in gaining knowledge of its weaknesses (both in terms of damage types, weak spots, and the openings during its moves). Of course, it's a live-action 3d game with a different design philosophy from CoC2, but my point is simply that to call it bad game design as a blanket statement is incorrect. It
can be bad design, but that's dependent on its implementation. I don't believe most players use consumables, but there is a purpose for their existence, in how they can deal alternative damage types, so that if you know the enemy's weaknesses, you can use it to make fights much easier. Even if you don't use or have consumables, you can still exploit weaknesses through equipment, powers, and companions, and if the foe is susceptible to tease you can use that rather than wade through the health pool.